Third Maximum Number

Given anon-emptyarray of integers, return thethirdmaximum 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.

Tips:

注意题目要求，要知道PQ不会自动查重，所以要用一个set。

Code：

public class Solution {
    public int thirdMax(int[] nums) {
        PriorityQueue<Integer> pq = new PriorityQueue<>();
        Set<Integer> set = new HashSet<>();
        for (int i : nums) {
            if (set.contains(i)) continue;
            pq.offer(i);
            set.add(i);
            if (pq.size() > 3) set.remove(pq.poll());
        }
        if (pq.size() < 3) {
            while (pq.size() > 1) pq.poll();
        }
        return pq.poll();
    }
}