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