Easy
May 23, 2025#arrays
#hashing
217. Contains Duplicate
Problem
Given an integer array nums, return true if any value appears at least twice in the array, and return false if every element is distinct.
Example 1:
Input: nums = [1,2,3,1]
Output: true
Explanation:
The element 1 occurs at the indices 0 and 3.
Example 2:
Input: nums = [1,2,3,4]
Output: false
Explanation:
All elements are distinct.
Example 3:
Input: nums = [1,1,1,3,3,4,3,2,4,2]
Output: true
Constraints:
- 1 <= nums.length <= 105
- -109 <= nums[i] <= 109
Approach
Simply use a hash map to keep track of which numbers we've already seen. If we've already seen a number, return true. Otherwise add to the hashmap and continue iterating. If we reach the end, there are no duplicates.
Complexity
Time: O(n)
We iterate through the array once
Space: O(n)
We create a hash map that can, at most, contain all the numbers