Contains Duplicate
Easy· hash set
Problem
Return true if any value appears at least twice in the array, and false if every element is distinct.
Examples
Input: nums = [7,1,3,7]
Output: true
7 appears at indices 0 and 3.
Input: nums = [1,2,3]
Output: false
Constraints
- • 1 <= nums.length <= 10^5
- • -10^9 <= nums[i] <= 10^9
Hints & approach
Hint 1
Sorting puts equal values next to each other, but costs O(n log n).
Hint 2
A set remembers everything you have seen with O(1) membership checks.
Approachtry the hints first
Walk the array and insert each value into a hash set. If a value is already in the set when you reach it, return true immediately. If the scan ends without a hit, all values are distinct. This is linear on average, at the cost of storing up to n values.
Time O(n) · Space O(n)