Given an integer array nums, return the largest integer that only occurs once. If no integer occurs once, return -1.
Example 1:
Input: nums = [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 is the answer.
Example 2:
Input: nums = [9,9,8,8] Output: -1 Explanation: There is no number that occurs only once.
Constraints:
1 <= nums.length <= 20000 <= nums[i] <= 1000