Leetcode学习笔记：#414. Third Maximum Number

Leetcode学习笔记：#414. 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).

实现：

public int thirdMax(int[] nums){
	PriorityQueue<Integer> pq = new PriorityQueue<>();
	Set<Integer> set = new HashSet<>();
	for(int i : nums){
		if(!set.contains(i)){
			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.peek();
}

思路：
用一个优先队列和set来遍历数组，如果队列大于三个，则更新队列，把最小的推出去，把比这个数字大的塞进来，再更新set，保持每个相同的数字只有一个。