Word Search (LeetCode 79)
The problem You get a grid of letters and a . Return if the word can be spelled…
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#python
388 posts
Word Search II (LeetCode 212)
The problem You get a grid of letters and a list of words. Return every word…
Walls and Gates (LeetCode 286)
The problem You get a grid where is a wall, is a gate, and (2147483647) is an…
Word Ladder (LeetCode 127)
The problem You get a word, an word and a list of allowed words . A…
Word Break (LeetCode 139)
The problem You get a string and a list of words . Return if can be cut into…
Valid Sudoku (LeetCode 36)
The problem You get a 9×9 Sudoku board as a list of lists of strings. Each cell…
Validate Binary Search Tree (LeetCode 98)
The problem You get the root of a binary tree. Return if it is a valid binary…
Valid Parenthesis String (LeetCode 678)
The problem You get a string of , and . Each can act as , as , or as nothing…
Valid Palindrome (LeetCode 125)
The problem You get a string that can contain letters, digits, spaces and…
Valid Parentheses (LeetCode 20)
The problem You get a string made only of the characters . Return if the…
Unique Paths II (LeetCode 63)
The problem You get an grid of 0s and 1s, where is an obstacle. A robot starts…
Valid Anagram (LeetCode 242)
The problem You get two strings and . Return if is an anagram of , meaning it…
Two Sum (LeetCode 1)
The problem You get an array of integers and an integer . Return the indices of…
Unique Paths (LeetCode 62)
The problem A robot starts at the top-left corner of an grid and wants to reach…
Two Sum II – Input Array Is Sorted (LeetCode 167)
The problem You get an array sorted in non-decreasing order and a . Exactly one…
Trapping Rain Water (LeetCode 42)
The problem You get an array of non-negative integers; each is the height of a…
Task Scheduler (LeetCode 621)
The problem You get a list of tasks, each a capital letter, and a cooldown . The…
Time Based Key-Value Store (LeetCode 981)
The problem Design a class with two methods: stores for at time . returns…
Swim in Rising Water (LeetCode 778)
The problem You get an grid where is the elevation of that cell; the values…
Surrounded Regions (LeetCode 130)
The problem You get a grid of and . A region of cells (connected up, down…
Swap Nodes in Pairs (LeetCode 24)
The problem You get the of a linked list. Swap every two adjacent nodes and…
Sum of Two Integers (LeetCode 371)
The problem Return for two integers without using the or operators. On…
Subtree of Another Tree (LeetCode 572)
The problem You get two binary trees, and . Return if contains a node whose…
Subsets (LeetCode 78)
The problem You get a list of distinct integers. Return every possible subset of…
Subsets (bitmask enumeration) (LeetCode 78)
The problem You get an array of distinct integers. Return every possible subset…
Subsets II (LeetCode 90)
The problem You get a list of integers that may contain duplicates. Return every…
Subarray Sums Divisible by K (LeetCode 974)
The problem Given an integer array (values may be negative) and an integer…
Subarray Sum Equals K (LeetCode 560)
The problem You get an integer array (values may be negative) and an integer…
Top K Frequent Elements (LeetCode 347)
The problem You get an integer array and an integer . Return the values that…
Student Attendance Record II (LeetCode 552)
The problem An attendance record is a string of (present), (absent) and (late…
Stone Game (LeetCode 877)
The problem Piles of stones sit in a row. Alice and Bob take turns, Alice first…
Squares of a Sorted Array (LeetCode 977)
The problem You get an integer array sorted in non-decreasing order. It may…
Split Array Largest Sum (LeetCode 410)
The problem You get an array of non-negative integers and an integer . Split…
Sort Colors (LeetCode 75)
The problem You get an array containing only , and (red, white and blue…
Spiral Matrix (LeetCode 54)
The problem You get an matrix. Return all its elements in clockwise spiral…
Sliding Window Maximum (LeetCode 239)
The problem You get an integer array and a window size . A window of…
Sort Characters By Frequency (LeetCode 451)
The problem You get a string . Rearrange it so that characters appear in order…
Snapshot Array (LeetCode 1146)
The problem Design an array of a given , initially all zeros, that can take…
Single Number III (LeetCode 260)
The problem You get an array where every value appears exactly twice, except two…
Single Number II (LeetCode 137)
The problem You get an array where every value appears exactly three times…
Shortest Path Visiting All Nodes (LeetCode 847)
The problem You get an undirected, connected graph with nodes as an adjacency…
Single Number (LeetCode 136)
The problem You get a non-empty array of integers. Every value appears exactly…
Shortest Palindrome (LeetCode 214)
The problem You get a string . You may add characters only to the front of it…
Short Encoding of Words (LeetCode 820)
The problem You want to encode a list of words as one string where each word is…
Set Matrix Zeroes (LeetCode 73)
The problem You get an matrix of integers. Wherever a cell is 0, set its entire…
Serialize and Deserialize Binary Tree (LeetCode 297)
The problem Design a with two methods: turns a binary tree into a string…
Search Insert Position (LeetCode 35)
The problem You get a sorted array of distinct integers and a . If is in the…
Search in Rotated Sorted Array (LeetCode 33)
The problem An array of distinct integers was sorted in ascending order and then…
Search a 2D Matrix (LeetCode 74)
The problem You get an integer matrix with two properties: each row is sorted…
Search Suggestions System (LeetCode 1268)
The problem You get a list of product names and a search word that the user…
Rotting Oranges (LeetCode 994)
The problem You get an grid where each cell is (empty), (fresh orange) or…
Same Tree (LeetCode 100)
The problem You get the roots and of two binary trees. Return if they are the…
Rotate List (LeetCode 61)
The problem You get the of a linked list and a non-negative integer . Rotate…
Roman to Integer (LeetCode 13)
The problem You get a valid Roman numeral as a string made of (1, 5, 10, 5…
Reverse Linked List II (LeetCode 92)
The problem You get the of a linked list and two 1-indexed positions . Reverse…
Reverse Linked List (LeetCode 206)
The problem You get the of a singly linked list. Reverse the list so the last…
Rotate Image (LeetCode 48)
The problem You get a square matrix. Rotate it 90° clockwise in place: you must…
Reverse Nodes in k-Group (LeetCode 25)
The problem You get the of a linked list and a positive integer . Reverse the…
Reverse Words in a String (LeetCode 151)
The problem You get a string of words separated by spaces. Return the words in…
Repeated Substring Pattern (LeetCode 459)
The problem Given a string , decide whether it can be built by writing some…
Reverse Integer (LeetCode 7)
The problem You get a signed 32-bit integer . Return it with its digits reversed…
Repeated String Match (LeetCode 686)
The problem You get two strings and . Return the smallest number of times you…
Replace Words (LeetCode 648)
The problem You get a list of roots (the dictionary) and a sentence of space…
Reorganize String (LeetCode 767)
The problem You get a string of lowercase letters. Rearrange its letters so…
Repeated DNA Sequences (LeetCode 187)
The problem A DNA string uses only the letters , , and . Return every…
Reverse Bits (LeetCode 190)
The problem You get a 32-bit unsigned integer . Reverse the order of its 32 bits…
Reorder List (LeetCode 143)
The problem You get the of a singly linked list . Rearrange it in place into…
Remove Nth Node From End of List (LeetCode 19)
The problem You get the of a singly linked list and an integer . Remove the n…
Remove K Digits (LeetCode 402)
The problem You get a non-negative integer as a string and an integer . Remove…
Remove Duplicates from Sorted Array (LeetCode 26)
The problem You get an integer array sorted in non-decreasing order. Rearrange…
Remove Duplicates from Sorted List II (LeetCode 82)
The problem You get the of a linked list sorted in ascending order. Remove…
Regular Expression Matching (LeetCode 10)
The problem Implement matching for a pattern against a string , where: matches…
Remove Covered Intervals (LeetCode 1288)
The problem You get a list of intervals . Interval is covered by if and…
Reconstruct Itinerary (LeetCode 332)
The problem You get a list of airline tickets . Build the itinerary that starts…
Ransom Note (LeetCode 383)
The problem You get two strings, and . Each letter in the magazine can be used…
Redundant Connection (LeetCode 684)
The problem You start with a tree on nodes to , then one extra edge is added…
Range Sum Query - Immutable (LeetCode 303)
The problem You are given an integer array that never changes. Build a class…
Product of the Last K Numbers (LeetCode 1352)
The problem Design a class that receives a stream of non-negative integers…
Range Sum Query 2D - Immutable (LeetCode 304)
The problem You are given a matrix of integers that never changes. Build a class…
Product of Array Except Self (LeetCode 238)
The problem Given an integer array , return an array where is the product of…
Permutations (LeetCode 46)
The problem You get a list of distinct integers. Return every possible ordering…
Pow(x, n) (LeetCode 50)
The problem Implement : raise a floating-point number to an integer power…
Permutations II (LeetCode 47)
The problem You get a list of integers that may contain duplicates. Return every…
Plus One (LeetCode 66)
The problem A non-negative integer is stored as a list of its digits, most…
Populating Next Right Pointers in Each Node (LeetCode 116)
The problem You get a perfect binary tree: every internal node has exactly two…
Permutation in String (LeetCode 567)
The problem You get two strings and . Return if some contiguous piece of is a…
Path with Maximum Probability (LeetCode 1514)
The problem You get an undirected graph with nodes. Edge joins and succeeds…
Path With Minimum Effort (LeetCode 1631)
The problem You get a grid of . You start at the top-left cell and want to reach…
Path Sum (LeetCode 112)
The problem You get the root of a binary tree and an integer . Return if some…
Partition to K Equal Sum Subsets (LeetCode 698)
The problem You get an array of positive integers and a number . Decide whether…
Partition Equal Subset Sum (LeetCode 416)
The problem Given an array of positive integers, return if it can be split…
Partition Labels (LeetCode 763)
The problem Given a string of lowercase letters, split it into as many parts as…
Palindromic Substrings (LeetCode 647)
The problem Given a string , count how many of its substrings are palindromes…
Palindrome Partitioning (LeetCode 131)
The problem Given a string , cut it into one or more pieces so that every piece…
Palindrome Linked List (LeetCode 234)
The problem You get the of a singly linked list of integers. Return if the…
Partition Array for Maximum Sum (LeetCode 1043)
The problem You get an integer array and an integer . Cut the array into…
Number of Islands (LeetCode 200)
The problem You get a 2-D grid of (land) and (water). An island is a group of…
Online Stock Span (LeetCode 901)
The problem Design a class whose method is called once per day with that day’s…
Pacific Atlantic Water Flow (LeetCode 417)
The problem You get a grid of heights. The Pacific touches the top and left…
Number of 1 Bits (LeetCode 191)
The problem Given a non-negative integer (treated as an unsigned 32-bit value…
Non-overlapping Intervals (LeetCode 435)
The problem Given a list of intervals , return the minimum number of intervals…
Number of Connected Components (LeetCode 323)
The problem You get nodes labelled to and a list of undirected . Return how…
Odd Even Linked List (LeetCode 328)
The problem You get the of a linked list. Reorder it so all nodes at odd…
N-Queens (LeetCode 51 / 52)
The problem Place queens on an chessboard so that no two attack each other: no…
Next Greater Element II (LeetCode 503)
The problem You get an integer array that is circular: after the last element…
Next Greater Element I (LeetCode 496)
The problem You get two arrays of distinct integers, and , where every value in…
Network Delay Time (LeetCode 743)
The problem There are nodes labelled to . Each entry in is a directed edge…
My Calendar I (LeetCode 729)
The problem Design a calendar class with one method, . Each event is the half…
Multiply Strings (LeetCode 43)
The problem You get two non-negative integers as strings, and . Return their…
Missing Number (LeetCode 268)
The problem You get an array of distinct numbers taken from the range to…
Minimum Window Substring (LeetCode 76)
The problem You get two strings and . Return the shortest substring of that…
Move Zeroes (LeetCode 283)
The problem You get an integer array . Move all the s to the end in place, while…
Minimum Path Sum (LeetCode 64)
The problem You get an grid of non-negative numbers. Walk from the top-left…
Minimum Value to Get Positive Step by Step Sum (LeetCode 1413)
The problem You pick a positive integer , then add the numbers of to it one at…
Minimum Size Subarray Sum (LeetCode 209)
The problem You get an array of positive integers and a positive integer…
Minimum Cost to Cut a Stick (LeetCode 1547)
The problem A wooden stick has length , with positions to . You must make every…
Minimum Depth of Binary Tree (LeetCode 111)
The problem You get the of a binary tree. Return its minimum depth: the number…
Minimum Number of Arrows to Burst Balloons (LeetCode 452)
The problem Each balloon spans a horizontal range . An arrow shot straight up at…
Min Stack (LeetCode 155)
The problem Design a stack class with four operations, each in O(1) time: puts…
Merge Two Sorted Lists (LeetCode 21)
The problem You get the heads of two linked lists, each already sorted in non…
Middle of the Linked List (LeetCode 876)
The problem You get the of a singly linked list. Return the middle node. If the…
Merge k Sorted Lists (LeetCode 23)
The problem You get an array of linked lists, each sorted in ascending order…
Min Cost Climbing Stairs (LeetCode 746)
The problem You get an array , where is the price of stepping off step . You…
Min Cost to Connect All Points (LeetCode 1584)
The problem You get points on a 2-D plane. Connecting two points costs their…
Meeting Rooms (LeetCode 252)
The problem You get a list of meetings, each as . Decide whether one person can…
Merge Triplets to Form Target Triplet (LeetCode 1899)
The problem You get a list of triplets and a triplet. One operation picks two…
Meeting Rooms II (LeetCode 253)
The problem You get a list of meetings . Return the minimum number of conference…
Merge Intervals (LeetCode 56)
The problem Given a list of intervals , merge every group of overlapping…
Median of Two Sorted Arrays (LeetCode 4)
The problem You get two sorted arrays (length ) and (length ). Return the…
Maximum Subarray (LeetCode 53)
The problem Given an integer array (at least one element, values can be…
Maximum XOR of Two Numbers in an Array (LeetCode 421)
The problem You get an array of non-negative integers. Return the largest value…
Maximum Profit in Job Scheduling (LeetCode 1235)
The problem You get jobs. Job runs from to and pays . Choose a set of jobs…
Maximum Product Subarray (LeetCode 152)
The problem Given an integer array (at least one element; values may be…
Maximum Size Subarray Sum Equals k (LeetCode 325)
The problem Given an integer array (values can be negative) and an integer…
Maximum Depth of Binary Tree (LeetCode 104)
The problem You get the root of a binary tree. Return its maximum depth: the…
Maximum Average Subarray I (LeetCode 643)
The problem You get an integer array and an integer . Among all contiguous…
Maximal Square (LeetCode 221)
The problem You get a matrix of characters and . Find the largest square made…
Max Consecutive Ones III (LeetCode 1004)
The problem You get a binary array (only 0s and 1s) and an integer . You may…
Map Sum Pairs (LeetCode 677)
The problem Design a class: stores . If the key already exists, the new value…
LRU Cache (LeetCode 146)
The problem Design a class that stores up to key-value pairs and supports…
Majority Element (LeetCode 169)
The problem You get an array of length . One value, the majority element…
Lowest Common Ancestor of a BST (LeetCode 235)
The problem You get the root of a binary search tree and two values and that…
Longest Word in Dictionary (LeetCode 720)
The problem You get a list of words. Find the longest word that can be built one…
Lowest Common Ancestor of a Binary Tree (LeetCode 236)
The problem You get the root of a binary tree (not a BST) and two values and…
Longest Subarray of 1's After Deleting One Element (LeetCode 1493)
The problem You get a binary array . You must delete exactly one element. Return…
Longest Repeating Character Replacement (LeetCode 424)
The problem You get an uppercase string and an integer . You may change up to…
Longest Substring Without Repeating Characters (LeetCode 3)
The problem You get a string . Return the length of the longest substring…
Longest Palindromic Subsequence (LeetCode 516)
The problem Given a string (at least one character), return the length of its…
Longest Increasing Subsequence (LeetCode 300)
The problem Given an integer array , return the length of the longest strictly…
Longest Happy Prefix (LeetCode 1392)
The problem A happy prefix of a string is a non-empty prefix that is also a…
Longest Duplicate Substring (LeetCode 1044)
The problem Given a string of lowercase letters, return the longest substring…
Longest Palindromic Substring (LeetCode 5)
The problem Given a string , return its longest contiguous substring that reads…
Longest Consecutive Sequence (LeetCode 128)
The problem You get an unsorted array of integers . Return the length of the…
Longest Common Subsequence (LeetCode 1143)
The problem Given two strings and , return the length of their longest common…
Linked List Cycle II (LeetCode 142)
The problem You get the of a singly linked list that may contain a cycle…
Linked List Cycle (LeetCode 141)
The problem You get the of a singly linked list. Some node’s may point back to…
LFU Cache (LeetCode 460)
The problem Design a cache with a fixed that supports, in O(1) average time…
Longest Common Prefix (LeetCode 14)
The problem You get a list of strings. Return the longest string that is a…
Letter Combinations of a Phone Number (LeetCode 17)
The problem On an old phone keypad, each digit from 2 to 9 maps to a few letters…
Last Stone Weight (LeetCode 1046)
The problem You get a list of stone weights. Each turn, take the two heaviest…
Largest Rectangle in Histogram (LeetCode 84)
The problem You get an array of non-negative integers, the heights of bars in a…
Kth Largest Element in an Array (LeetCode 215)
The problem You get an integer array and an integer . Return the kth largest…
Kth Smallest Element in a BST (LeetCode 230)
The problem You get the root of a binary search tree and an integer (1-indexed…
Kth Largest Element in a Stream (LeetCode 703)
The problem Design a class . It starts with the numbers in . Each call to adds…
Koko Eating Bananas (LeetCode 875)
The problem There are of bananas, and is the size of pile . Koko picks an…
Isomorphic Strings (LeetCode 205)
The problem You get two strings and of the same length. They are isomorphic if…
K Closest Points to Origin (LeetCode 973)
The problem You get a list of points on a plane and an integer . Return the k…
Jump Game (LeetCode 55)
The problem You start at index 0 of an array of non-negative integers. is the…
Jump Game II (LeetCode 45)
The problem You stand at index 0 of an array . From index you may jump forward…
Invert Binary Tree (LeetCode 226)
The problem You get the root of a binary tree. Invert it, meaning produce its…
Intersection of Two Linked Lists (LeetCode 160)
The problem You get the heads of two singly linked lists, and . At some node…
Interleaving String (LeetCode 97)
The problem You get three strings , and . Return if can be formed by…
Interval List Intersections (LeetCode 986)
The problem You get two lists of closed intervals, and . Each list is sorted…
Insert Delete GetRandom O(1) (LeetCode 380)
The problem Design a with three operations, each in O(1) average time: : add…
Implement Trie (Prefix Tree) (LeetCode 208)
The problem Design a class with three methods: stores a word. returns only…
House Robber II (LeetCode 213)
The problem Same rules as House Robber: is the money in house , and you cannot…
House Robber III (LeetCode 337)
The problem Houses form a binary tree. Each node has a value (the money inside…
House Robber (LeetCode 198)
The problem Houses stand in a row and is the money in house (all values non…
Happy Number (LeetCode 202)
The problem Take a positive integer . Replace it with the sum of the squares of…
Hand of Straights (LeetCode 846)
The problem You hold a hand of cards, each with an integer value, and a number…
Gas Station (LeetCode 134)
The problem There are stations on a circular road. Station gives you fuel…
Graph Valid Tree (LeetCode 261)
The problem You get nodes labelled to and a list of undirected . Return if…
Generate Parentheses (LeetCode 22)
The problem Given , return every string of pairs of round brackets that is well…
Game of Life (LeetCode 289)
The problem You get an board of cells, each 1 (live) or 0 (dead). Every cell…
Insert Interval (LeetCode 57)
The problem You get a list of non-overlapping intervals sorted by start, and one…
Fruit Into Baskets (LeetCode 904)
The problem A row of trees is given as an array , where is the type of fruit on…
Find the Index of the First Occurrence in a String (LeetCode 28)
The problem You get two strings, and . Return the index where first appears…
Find the City With the Smallest Number of Neighbors (LeetCode 1334)
The problem There are cities numbered to , joined by weighted, undirected…
Find the Duplicate Number (LeetCode 287)
The problem You get an array of length . Every value is between and , and…
Find Pivot Index (LeetCode 724)
The problem Given an integer array , find the pivot index: the leftmost index…
Group Anagrams (LeetCode 49)
The problem You get a list of strings . Group together the words that are…
Find Peak Element (LeetCode 162)
The problem You get an integer array where no two neighbours are equal. A peak…
Find Minimum in Rotated Sorted Array (LeetCode 153)
The problem A sorted array of distinct integers has been rotated some number of…
Find K Pairs with Smallest Sums (LeetCode 373)
The problem You get two arrays and , both sorted in non-decreasing order, and…
Find All Anagrams in a String (LeetCode 438)
The problem You get a string and a pattern . Return the list of every start…
Find First and Last Position of Element in Sorted Array (LeetCode 34)
The problem You get an array sorted in non-decreasing order (duplicates allowed…
Encode and Decode Strings (LeetCode 271)
The problem Design two functions. turns a list of strings into a single string…
First Bad Version (LeetCode 278)
The problem You have versions of a product. At some point one version went bad…
Evaluate Reverse Polish Notation (LeetCode 150)
The problem You get a list of string tokens that form an arithmetic expression…
Employee Free Time (LeetCode 759)
The problem You get each employee’s working schedule as a sorted list of non…
Edit Distance (LeetCode 72)
The problem Given two words and , return the minimum number of single-character…
Find Median from Data Stream (LeetCode 295)
The problem Design a class with two methods: adds a number from the stream…
Dungeon Game (LeetCode 174)
The problem A knight starts at the top-left of a grid and must reach the…
First Unique Character in a String (LeetCode 387)
The problem You get a string of lowercase letters. Return the index of the…
Diameter of Binary Tree (LeetCode 543)
The problem You get the root of a binary tree. Return its diameter: the number…
Distinct Subsequences (LeetCode 115)
The problem Given strings and , return the number of distinct ways to pick…
Design Underground System (LeetCode 1396)
The problem Design a system that tracks passengers on a metro network…
Design Circular Queue (LeetCode 622)
The problem Design a circular queue with a fixed capacity . Support: : add at…
Design Twitter (LeetCode 355)
The problem Design a simplified Twitter with four operations: : the user posts a…
Design Add and Search Words Data Structure (LeetCode 211)
The problem Design a with two methods: stores a word of lowercase letters…
Decode Ways (LeetCode 91)
The problem Letters are encoded as numbers: , , …, . Given a string of digits…
Design HashMap (LeetCode 706)
The problem Implement a hash map for integer keys and values without using any…
Critical Connections in a Network (LeetCode 1192)
The problem There are servers, numbered to , joined by undirected connections…
Daily Temperatures (LeetCode 739)
The problem You get an array of daily temperatures. For each day , return how…
Cousins in Binary Tree (LeetCode 993)
The problem You get the of a binary tree with unique values, and two different…
Course Schedule (LeetCode 207)
The problem There are courses labelled to . Each pair in means “you must…
Course Schedule II (LeetCode 210)
The problem There are courses labelled to . Each pair means “take before…
Count Vowels Permutation (LeetCode 1220)
The problem Count the strings of length built from the vowels that follow…
Continuous Subarray Sum (LeetCode 523)
The problem Given an array of non-negative integers and an integer , return if…
Contiguous Array (LeetCode 525)
The problem Given a binary array (only 0s and 1s), return the length of the…
Copy List with Random Pointer (LeetCode 138)
The problem Each node in a linked list has a , a pointer, and a pointer that…
Container With Most Water (LeetCode 11)
The problem You get an array where is the height of a vertical wall at…
Counting Bits (LeetCode 338)
The problem Given an integer , return a list of length where is the number of…
Construct Binary Tree from Preorder and Inorder (LeetCode 105)
The problem You get two lists for the same binary tree: its preorder traversal…
Combination Sum II (LeetCode 40)
The problem You get a list of positive integers , which may contain duplicates…
Combination Sum (LeetCode 39)
The problem You get a list of distinct positive integers and a . Return every…
Combinations (LeetCode 77)
The problem Given two integers and , return every way to choose distinct…
Climbing Stairs (LeetCode 70)
The problem You are at the bottom of a staircase with steps. Each move climbs…
Cheapest Flights Within K Stops (LeetCode 787)
The problem There are cities and a list of , each (one-way). Find the cheapest…
Circular Array Loop (LeetCode 457)
The problem You get a circular array of non-zero integers. Standing on index…
Coin Change (LeetCode 322)
The problem You get a list of coin denominations (unlimited supply of each) and…
Contains Duplicate (LeetCode 217)
The problem You get an array of integers . Return if any value appears at least…
Car Pooling (LeetCode 1094)
The problem A car with empty seats drives in one direction. Each trip is : pick…
Capacity To Ship Packages Within D Days (LeetCode 1011)
The problem Packages on a conveyor belt have weights and must be shipped in…
Candy (LeetCode 135)
The problem Children stand in a line, each with a rating. Give out candies so…
Bitwise AND of Numbers Range (LeetCode 201)
The problem Given two integers (both between 0 and 2³¹ − 1), return the bitwise…
Burst Balloons (LeetCode 312)
The problem Balloons in a row each carry a number. Bursting balloon earns…
Binary Tree Zigzag Level Order Traversal (LeetCode 103)
The problem You get the of a binary tree. Return its values level by level, but…
Binary Tree Maximum Path Sum (LeetCode 124)
The problem You get the root of a binary tree whose values can be negative. A…
Binary Tree Right Side View (LeetCode 199)
The problem You get the of a binary tree. Imagine standing to its right and…
Best Time to Buy and Sell Stock (LeetCode 121)
The problem You get an array where is a stock’s price on day . You may buy…
Binary Tree Level Order Traversal (LeetCode 102)
The problem You get the of a binary tree. Return its values level by level…
Coin Change II (LeetCode 518)
The problem You get an and a list of coin denominations (unlimited supply of…
Binary Tree Level Order Traversal II (LeetCode 107)
The problem You get the of a binary tree. Return its values level by level, but…
Backspace String Compare (LeetCode 844)
The problem You get two strings and that were typed into a text editor. The…
Average of Levels in Binary Tree (LeetCode 637)
The problem You get the of a non-empty binary tree. Return a list where the -th…
Assign Cookies (LeetCode 455)
The problem Each child has a greed factor : the smallest cookie size that makes…
Asteroid Collision (LeetCode 735)
The problem You get an array of non-zero integers, each an asteroid in a row…
Alien Dictionary (LeetCode 269)
The problem An alien language uses lowercase English letters in an unknown order…
Binary Search (LeetCode 704)
The problem You get an array of distinct integers sorted in ascending order…
4Sum (LeetCode 18)
The problem You get an integer array and a . Return every unique quadruplet…
Add Two Numbers (LeetCode 2)
The problem Two non-negative integers are stored as linked lists, one digit per…
Accounts Merge (LeetCode 721)
The problem You get a list of accounts. Each account is a name followed by one…
3Sum (LeetCode 15)
The problem You get an integer array . Return every unique triplet of values…
3Sum Closest (LeetCode 16)
The problem You get an integer array (at least three numbers) and a . Choose…
Coding Interview Patterns — Crack the Coding Round
There are thousands of coding-interview questions but only about eighteen…
Futures & Commodities Trading for Programmers
This is the third course in the trading-for-programmers set, alongside Options…
Crypto Options & Algo Trading for Programmers
If you have done the Options Trading for Programmers course, this is its wild…
Build a Futures Algo: A Trend System, End to End
The capstone. We take the whole course — the linear payoff, cost of carry…
Data & Tooling: Broker APIs and the Continuous-Contract Trap
Finally, the part that is ours. The futures stack is mostly the same as any…
Directional Strategies: Trend, Breakout & Mean Reversion
With the mechanics understood, we can run actual strategies. Futures are a…
Pricing & Basis: Cost of Carry, Contango & Backwardation
Why does a Nifty future trade at 24,138 when the index is at 24,000? Not magic…
Futures Basics: Long, Short, Contract Specs & the Linear Payoff
This lesson is the vocabulary and mechanics you must own. Futures are simpler…
Build a Crypto Algo: A Delta-Neutral Funding Bot, End to End
This is the capstone. We assemble the whole course — market structure, perps…
Design a Data Structure
Some interview questions don’t ask you to solve a problem — they ask you to…
Design a Data Structure — Practice Problems
Ten problems that drill the design-a-data-structure pattern from Lesson 27. Each…
Your Study Plan: Blind 75, NeetCode 150 & an 8-Week Schedule
You now have the whole toolkit — 24 patterns, each with a template, a diagram…
String Algorithms: KMP & Rabin-Karp
This is the advanced end of the string toolkit. Most string problems are solved…
Math & Geometry — Practice Problems
Ten problems that drill the math & geometry pattern from Lesson 26 — the in…
Math & Geometry
Most interview questions are about data structures. This small but reliable…
Advanced Dynamic Programming
By now you can define a state and a recurrence (Lessons 17–18). The DP problems…
Advanced Graphs — Practice Problems
Ten problems that drill the weighted-graph algorithms from Lesson 23. The…
String Algorithms — Practice Problems
Ten problems that drill KMP’s prefix function and Rabin-Karp’s rolling hash from…
Advanced DP — Practice Problems
Ten problems that drill bitmask, interval, and tree DP from Lesson 24. The work…
Greedy Algorithms — Practice Problems
Eleven problems that drill the greedy pattern from Lesson 22. The real exercise…
Advanced Graphs: Weighted Paths & MST
Lessons 12–16 covered unweighted graphs, where BFS gives the shortest path…
Bit Manipulation
Bit manipulation looks like a dark art, but it is really just one idea — an…
Greedy Algorithms
Greedy is the most dangerous pattern: the code is short and obvious, which makes…
Tries — Practice Problems
Ten problems that drill the trie pattern from Lesson 20. Build the dict-of-dicts…
Bit Manipulation — Practice Problems
Ten problems that drill the bit manipulation tricks from Lesson 21. The whole…
Tries (Prefix Trees)
A hash set can tell you whether an exact word exists, but it is useless the…
Data Structures: Your Toolbox
Part II of this course goes beyond the core 18 patterns into the structures and…
Dynamic Programming I (1-D) — Practice Problems
Thirteen problems that drill 1-D dynamic programming from Lesson 17. The hard 9…
Dynamic Programming II (2-D) — Practice Problems
Twelve problems that drill 2-D dynamic programming from Lesson 18 — two-sequence…
Dynamic Programming I — 1-D
Dynamic programming scares people more than anything else — but it’s a single…
Graphs: BFS, DFS, Topological Sort, Union-Find
Graphs look intimidating, but interview graph problems reduce to four tools on…
Dynamic Programming II — 2-D
The final pattern. When a problem involves two sequences or a grid, one index…
Backtracking (Try, Recurse, Undo)
Backtracking is how you systematically explore all possibilities — generate…
Heaps / Top-K — Practice Problems
Eleven problems that drill heaps / top-K from Lesson 14. The one trick to burn…
Tree DFS (Recurse, Combine, Return)
If BFS is for levels, DFS is for paths and subtrees — and almost every tree DFS…
Heaps / Top-K / Two Heaps
When you need the biggest or smallest few — but not a full sort — a heap is the…
Tree BFS (Level-Order Traversal)
When a tree (or grid) problem is about levels or shortest distance, you want BFS…
Graphs — Practice Problems
Twelve problems that drill the graph toolkit from Lesson 16 — DFS, BFS…
Linked-List In-Place Reversal
Linked-list questions scare people, but almost all of them come down to one…
Binary Search
Everyone knows binary search on a sorted array. The reason it’s a pattern worth…
Binary Search — Practice Problems
Thirteen problems that drill the binary-search pattern from Lesson 10 — the…
Tree BFS — Practice Problems
Ten problems that drill the breadth-first search / level-order pattern from…
Backtracking — Practice Problems
Twelve problems that drill backtracking from Lesson 15. They all run the same…
Linked-List Reversal — Practice Problems
Ten problems that drill the linked-list reversal / pointer-surgery pattern from…
Tree DFS — Practice Problems
Thirteen problems that drill tree DFS from Lesson 13. The skill is recursion…
Merge Intervals — Practice Problems
Ten problems that drill the merge-intervals pattern from Lesson 8. The recipe is…
Prefix Sums — Practice Problems
Ten problems that drill the prefix-sum pattern from Lesson 7. The big idea keeps…
Monotonic Stack — Practice Problems
Eleven problems that drill the stack and monotonic-stack pattern from Lesson…
Prefix Sums
Prefix sums are a quiet superpower: a tiny O(n) precomputation that makes every…
Hash Maps & Frequency — Practice Problems
Thirteen problems that drill the hash map & frequency pattern from Lesson 6. The…
Merge Intervals
Any time you see pairs and the word “overlapping”, this is your pattern. The…
Fast & Slow Pointers — Practice Problems
Ten problems that drill the fast & slow pointer pattern (Floyd’s tortoise-and…
Sliding Window — Practice Problems
Twelve problems that drill the sliding-window pattern from Lesson 4. The reps…
Sliding Window
Sliding window is two pointers’ close cousin, specialised for contiguous sub…
Fast & Slow Pointers
Fast & slow pointers (Floyd’s “tortoise and hare”) is a small, elegant trick…
Hash Maps & Frequency Counting
The hash map is the most useful data structure in interviews. The core move is…
Monotonic Stack
The monotonic stack is the pattern people find magical: a plain stack, kept in…
Two Pointers
Two pointers is the first pattern to master — it is simple, it appears…
Two Pointers — Practice Problems
Twelve problems that drill the two-pointer pattern from Lesson 3. The reps are…
Options Trading for Programmers — A Fundamentals Course
Most options content online is either hand-wavy “buy this call and get rich…
The Data & Tooling Stack: Where Coders Win
Finally, the part that is ours. Everything so far — the maths, the strategies…
Build a Simple Options Algo, End to End
This is the capstone. We take everything — the basics, the Greeks, pricing…
The Greeks: How an Option's Price Moves
An option’s price depends on several inputs — spot, strike, time, volatility…
Volatility: Historical vs Implied, IV Rank, Smile & India VIX
Options are really instruments for trading volatility, so this lesson earns its…
Pricing & Implied Volatility: Black-Scholes in Python
Here is where the programmer’s edge really shows. The pricing of an option…
Moneyness & Payoffs: ITM/ATM/OTM and the Four Shapes
Two ideas in this lesson — moneyness and payoffs — and once they are in your…
Building an AI FAANG Interview Coach: Run the Code, Don't Let the LLM Grade It
Ask ChatGPT to “review this solution and tell me if I’d pass the interview” and…
Building an AI Astrology (Kundali) Chatbot: Let the LLM Talk, Let the Ephemeris Do the Math
Ask ChatGPT “where was Saturn when I was born, 2:30 pm on 15 August 1990 in New…
Execution Algorithms: VWAP & TWAP in Python
Every strategy so far produced signals — when to be long, short, or flat. But a…
Position Sizing & the Kelly Criterion in Python
Every strategy article so far asked ”what should I trade?” This one asks the…
Order-Book Imbalance: A Microstructure Signal (in Python)
The strategies so far used daily or minute bars. This last one goes down to the…
The Moving-Average Crossover, Backtested Honestly in Python
If algo trading has a “hello world,” it’s the moving-average crossover. Every…
Momentum & Trend Following in Python
Momentum is, along with value, one of the most robust and widely-documented…
Mean Reversion & Pairs Trading in Python
The moving-average crossover bet on direction and lost. Here’s a strategy with a…
Market Making Basics: Spread Capture vs Inventory Risk (in Python)
So far you’ve been a taker — crossing the spread to get filled. A market maker…
Market Data: Types & Where to Download It (Free and Paid)
Data is the raw material of every strategy, and getting the right data is the…
Low-Latency Trading Systems & Algo Trading — From the Order Book to a Live Retail Algo
Almost everything written about high-frequency trading is either breathless…
Low-Latency Implementation
“Low latency” sounds like it should be about exotic tricks, but most of it is…
The Payment State Machine — Modelling Status and Handling Pending
On a payments team I worked with, the table had a column called . Over three…
Idempotency, Retries and Webhooks — Never Charge Twice
Here’s a bug I helped debug at a mid-sized ed-tech company. Some students were…
Integrating a Payment Gateway the Right Way
When I review payment integrations, I usually find the same three or four…
UPI for Engineers — Intent, QR, Pending and Reversals
One evening during an IPL final, our support queue suddenly had 300 tickets with…
AI Agent Development — From First Loop to Production
Every second LinkedIn post today is about AI agents. Most of them show a demo…
Capstone: Ship a Production Support Agent, End to End
We’ve covered a lot over eleven lessons. In this one, I want to walk through how…
Evaluating AI Agents — Outcomes, Trajectories, and CI Gates
Here’s a conversation I’ve had, in some form, with almost every team building…
Memory and Context Management for Agents
When the first million-token context windows arrived, a friend of mine (very…
Designing Tools Agents Can Actually Use
When an agent misbehaves, the first instinct is to fiddle with the system prompt…
Planning and Multi-Agent Patterns That Actually Work
There’s a type of architecture diagram I’ve started to dread. It has a “CEO…
The Agent Loop from Scratch — No Framework, Just Python
In the last lesson I said an agent is “an LLM in a loop choosing tools”. Today…
Learn Python — A Crash Course for Programmers
You already know how to program. You know loops, conditionals, functions, and…
Error Handling, File I/O & Context Managers
Python’s error handling has two ideas you won’t find in most languages: the…
Modules, Packages & Virtual Environments
Python’s module system is straightforward once you understand the mechanics…
Standard Library Power Tools & Common Patterns
Python ships with an absurdly complete standard library — “batteries included…
OOP in Python — Classes, Inheritance & Magic Methods
Python’s OOP is fundamentally different from Java or C++. There are no access…
Functions, Decorators & Generators
Functions in Python are objects. You can pass them around, store them in…
Python Syntax & Data Types for Programmers
If you already know another language, half of Python will feel familiar. The…
Building an AI Voicebot for Visitor Check-In — A Practical Guide to Handling the Messy Parts
Every office lobby has the same problem: a visitor walks in, nobody’s at the…
Jenkins Pipeline with Jenkinsfile - How To Schedule Job on Cron and Not on Code Commit
Introduction In this post we will see following: How to schedule a job on cron…
How to Fetch Multiple Credentials and Expose them in Environment using Jenkinsfile pipeline
Introduction In this post, we will see how to fetch multiple credentials and…
Jenkins Pipeline - How to run Automation on Different Environment (Dev/Stage/Prod), with Credentials
Introduction I have an automation script, that I want to run on different…
Jenkinsfile - How to Create UI Form Text fields, Drop-down and Run for Different Conditions
Introduction I had to write a CICD system for one of our project. I had to…
How to Git Clone Another Repository from Jenkin Pipeline in Jenkinsfile
Introduction There are some cases, where I need another git repository while…
Python SMTP Email Code - How to Send HTML Email from Python Code with Authentication at SMTP Server
Introduction This post has the complete code to send email through smtp server…
Python SMTP Email Code - Sender Address Rejected - Not Owned By User
Introduction In a normal email sending code from python, I’m getting following…
Nodejs with MongoDB - Number of Opened Connections Keep on Increasing with Mongoose Library
Introduction In one of my app, I was using to talk to . I have used some event…
Django Python - How to Build Docker Image and Run Web-service on Apache with Python 3.9
Introduction So you have a Django project, and want to run it using docker image…
Python Build Quality Gates with Pylint and Unittest Coverage Thresholds
Introduction It is very important to introduce few process so that your code and…
A Jenkins Groovy Pipeline for Building Python Projects and Pushing to Artifactory
Introduction In this post, we will see a sample Jenkin Pipeline Groovy script…
Python - How to Implement Timed-Function which gets Timeout After Specified Max Timeout Value
Introduction We often require to execute in timed manner, i.e. to specify a max…
How to Solve Circular Import Error in Python
Introduction To give some context, I have two python files. (Both in same folder…
Python Code - How To Read CSV with Headers into an Array of Dictionary
Introduction Lets assume we have a csv something similar to following: Python…
Python Code - How To Read CSV into an Array of Arrays
Introduction In last post, we saw How to read CSV with Headers into Dictionary…
Install Private Artifactory Modules Securely in a Python Docker Build
Introduction I was having a private artifactory, and has my custom modules…
Dockerfile for building Python 3.9.2 and Openssl for FIPS
Introduction In previous posts, we saw how to build FIPS enabled Openssl, and…
Python - Some useful Pytest Commands
Introduction In this post, we will explore some useful command line options for…
Python - How to apply patch to Python and Install Python via Pyenv
Introduction In this post, we will see how we can apply a patch to Python and…
How to Install Python from command line and Docker on Windows
Introduction We will see how we can install Python 3.7 on Windows without UI. i…
How to Install Python from command line and Docker on Linux
Introduction We will see how we can install Python from command line using pyenv…
How to Patch and Build Python 3.9.x for FIPS enabled Openssl
Introduction In this post, we will see Python 3.9.x patch for FIPS enabled…
How to Patch and Build Python 3.7.9 for FIPS enabled Openssl
Introduction In this post, we will see Python 3.7.9 patch for FIPS enabled…
How to build FIPS enabled Openssl in docker
Introduction In this post, we will see how we can build FIPS enabled openssl in…
Python - How to read files in multiple ways
Read file all in one shot Above code read whole file at once, but if the files…
List and Download Azure Storage Blobs in Python Without the Azure SDK
Introduction In this tutorial we will see, How to list and download storage…
List and Download Azure Storage Blobs in Python with the Official Azure SDK
Introduction In this tutorial we will see: How to instantiate different classes…
Implement a command line shell by using Command Dispatcher in Python
Lets implement a command shell by using a command dispatcher. The objective is…
Multithreading in Python, Lets clear the confusion between Multithreading and Multiprocessing
So, you want to run your code in parallel so that your can process faster, or…
Implementation of Timeit function, Get performance numbers for a function
This is regarding the timeit implementation in python. The basic requirement…
Python 3 - Magical Methods and Tricks with extremely useful methods
This post will show some really awesome tricks in python. Get the power of a…
Python 3 - Fun with Python String
This post some useful tips of using strings, and some issues while dealing with…
Python 3 - Format String fun
This post is dedicated for cases where we intend to append a variable value in a…
Understanding and Solving pylint errors for Python 3
Pylint is an excellent tool to have good quality code. This post is not about…
Python: How to generate string of arbitrary length of any alphabet characters
I was testing a bug where a field was limited to 255 characters only. I needed…
Python - Dont Use Static or Class variables with Self
While doing code review of one of junior, I encountered following code: What…