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4. Remove Duplicates from Sorted Array

easyAsked at Wix

Remove duplicates from a sorted array in-place; Wix uses two pointers for deduplicating ordered template-component IDs.

By Alex Chen, Founder, InterviewChamp.AI · Last verified

Problem

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

Constraints

  • 1 <= nums.length <= 3 * 10^4
  • nums is sorted non-decreasing

Examples

Example 1

Input
nums=[1,1,2]
Output
2 (nums=[1,2,_])

Example 2

Input
nums=[0,0,1,1,1,2,2,3,3,4]
Output
5

Approaches

1. Brute force

Use a Set, copy unique back.

Time
O(n)
Space
O(n)
const s=[...new Set(nums)]; for(let i=0;i<s.length;i++) nums[i]=s[i]; return s.length;

Tradeoff:

2. Two pointers

Write pointer advances only when a new value appears.

Time
O(n)
Space
O(1)
function removeDuplicates(nums){
  if(!nums.length) return 0;
  let k=1;
  for(let i=1;i<nums.length;i++){
    if(nums[i]!==nums[i-1]) nums[k++]=nums[i];
  }
  return k;
}

Tradeoff:

Wix-specific tips

Wix expects you to call out the in-place memory win — a relevant constraint when serializing builder JSON back to their multi-tenant storage.

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