ContainsDuplicate.java

import java.util.HashMap;

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// 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.

// Example 1:

// Input: [1,2,3,1]
// Output: true
// Example 2:

// Input: [1,2,3,4]
// Output: false
// Example 3:

// Input: [1,1,1,3,3,4,3,2,4,2]
// Output: true


class Solution {
  public boolean containsDuplicate(int[] nums) {
    if (nums.length == 0 || nums.length == 1) { return false; }

    HashMap<Integer, Integer> numToCount = new HashMap<>();
    for (int num : nums) {
      if (numToCount.containsKey(num) && numToCount.get(num) == 1) {
        return true;
      } else {
        numToCount.put(num, 1);
      }
    }

    return false;
  }
}