Largest Unique Number

Given an array of integers A, return the largest integer that only occurs once.

If no integer occurs once, return -1.

 

Example 1:

Input: [5,7,3,9,4,9,8,3,1]
Output: 8
Explanation: 
The maximum integer in the array is 9 but it is repeated. The number 8 occurs only once, so it's the answer.
Example 2:

Input: [9,9,8,8]
Output: -1
Explanation: 
There is no number that occurs only once.
 

Note:

  1. 1 <= A.length <= 2000
  2. 0 <= A[i] <= 1000

Solution:

class Solution {
    public int largestUniqueNumber(int[] A) {
        Map<Integer, Integer> map = new HashMap();
        for (int val : A) {
            map.put(val, map.getOrDefault(val, 0) + 1);
        }
        int max = -1;
        for (Map.Entry<Integer, Integer> entry : map.entrySet()) {
            if (entry.getValue() == 1 && entry.getKey() > max) {
                max = entry.getKey();
            }
        }
        return max;
    }
}