217. Contains Duplicate

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

Example 2:

Input: nums = [1,2,3,4]

Output: false

Approach

Loop over the array and add check whether Set already contains the element, if so duplicate exists else, add to Set and continue. If loop is finished it means no duplicate element exists.

Code

public boolean containsDuplicate(int[] nums) {
  Set<Integer> set = new HashSet<Integer>();

  for (int num : nums) {
    if (set.contains(num)) {
      return true;
    }
    set.add(num);
  }
  return false;
}

Time Complexity	Space Complexity
\(\mathcal{O}(n)\)	\(\mathcal{O}(n)\)