Remove Duplicates from Sorted Array - Leet Code Solution

Problem Statement

Given a sorted array nums, remove the duplicates in-place such that each element appear only once and return the new length.

Note:

We have to return the new length
And, modify the array also

Constraint
Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.

Examples

# Example 1
   Given nums = [1,1,2],
   Output = 2

# Example 2
   Given nums = [0,0,1,1,1,2,2,3,3,4],
   Output = 5

Solution (Using an extra variable)

First think out loud about the problem.

Its a sorted array,
And, which means a number which is repeating would occur later after another number.

Code

Lets look at the code

public int removeDuplicates(int[] nums) {
   if (nums == null || nums.length == 0) {
      return 0;
   }
   int num = nums[0];
   int j=1;
   
   for (int i=1; i<nums.length; i++) {
      if (num != nums[i]) {
         num = nums[i];
         
         nums[j] = nums[i];
         j ++;
      }
   }
   
   return j;
   }

Steps

We can begin with first index value, save it in a variable.
We can keep another variable for storing our index j, which will point to index upto which our array is unique.
This index variable will increment after finding a unique value only.
And, we need to copy that unique value to our array as well.

Results

Runtime: 0 ms, faster than 100.00% of Java online submissions for Remove Duplicates from Sorted Array.
Memory Usage: 41.1 MB, less than 87.80% of Java online submissions for Remove Duplicates from Sorted Array.

Code without extra variable

public int removeDuplicates2(int[] nums) {
   if (nums == null || nums.length == 0) {
      return 0;
   }
   int j=1;
   for (int i=1; i<nums.length; i++) {
      if (nums[j-1]!= nums[i]) {
         nums[j]= nums[i];
         
         j ++;
      }
   }
   
   return j;
   }