Contains Duplicate

Source

1. leetcode

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.

Analysis

Simply add numbers seen before into a hash set, and whenever meet a new number, juged whether it is already in the set or not.

Complexity

Time: O(N)

Space: O(N)

Code

Java

public class Solution {
  public boolean containsDuplicate(int[] nums) {
    Set<Integer> appearedSet = new HashSet<>();
    for (int num : nums) {
      if (!appearedSet.add(num)) {
        return true;
      }
    }
    return false;
  }
}