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10. Contains Duplicate

easyAsked at ByteDance

Return true if any value appears twice in the array — ByteDance uses it as a dedup warm-up before deeper content-fingerprinting questions.

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

Problem

Given an integer array nums, return true if any value appears at least twice and return false if every element is distinct.

Constraints

  • 1 <= nums.length <= 10^5
  • -10^9 <= nums[i] <= 10^9

Examples

Example 1

Input
nums = [1,2,3,1]
Output
true

Example 2

Input
nums = [1,2,3,4]
Output
false

Approaches

1. Sort and compare neighbors

Sort the array and look for any adjacent duplicates.

Time
O(n log n)
Space
O(1)
nums.sort((a,b)=>a-b);
for(let i=1;i<nums.length;i++) if(nums[i]===nums[i-1]) return true;
return false;

Tradeoff:

2. Hash set

Stream through nums; bail the moment a value is already in the set.

Time
O(n)
Space
O(n)
function containsDuplicate(nums) {
  const seen = new Set();
  for (const n of nums) {
    if (seen.has(n)) return true;
    seen.add(n);
  }
  return false;
}

Tradeoff:

ByteDance-specific tips

ByteDance reviewers reward the framing that this is the simplest possible dedup, which ties directly to how their video-upload pipeline rejects re-uploaded clips by perceptual hash.

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Output

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