Third Maximum Number

Given a non-empty array of integers, return the third maximum number in this array. If it does not exist, return the maximum number. The time complexity must be in O(n).

Example 1:

Input: [3, 2, 1]

Output: 1

Explanation: The third maximum is 1.

Example 2:

Input: [1, 2]

Output: 2

Explanation: The third maximum does not exist, so the maximum (2) is returned instead.

Example 3:

Input: [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.

class Solution {
public:
    int thirdMax(vector<int>& nums) {
        set<int> container;
        for (int number : nums) {
            container.insert(number);
        }
        
        auto ite = container.rbegin();
        if (container.size() < 3) return *ite;
        ite++; ite++;
        return *ite;
    }
};