217. Contains Duplicate

Given an array of integers, find if the array contains any duplicates. Your function should return true if any value appears at least twice in the array, and it should return false if every element is distinct.



Solution:

Use a HashSet to store the one we checked.

If the number is in the HashSet, we found the duplicate and return true.

The time complexity is O(n) and space complexity is O(n) as well.



Code:

public class Solution {
    public boolean containsDuplicate(int[] nums) {
        if (nums == null || nums.length == 0) {
            return false;
        }
        HashSet<Integer> hash = new HashSet<>();
        for (int i = 0; i < nums.length; i++) {
            if (hash.contains(nums[i])) {
                return true;
            }
            hash.add(nums[i]);
        }
        return false;
    }
}