Given integer array
nums, return the third maximum number in this array. If the third maximum does not exist, return the maximum number.
Input: nums = [3,2,1] Output: 1 Explanation: The third maximum is 1.
Input: nums = [1,2] Output: 2 Explanation: The third maximum does not exist, so the maximum (2) is returned instead.
Input: nums = [2,2,3,1] Output: 1 Explanation: Note that the third maximum here means the third maximum distinct number. Both numbers with value 2 are both considered as second maximum.
1 <= nums.length <= 104
-231 <= nums[i] <= 231 - 1
Follow up: Can you find an