LeetCode-面试题59 - II. 队列的最大值

请定义一个队列并实现函数 max_value 得到队列里的最大值，要求函数max_value、push_back 和 pop_front 的均摊时间复杂度都是O(1)。

若队列为空，pop_front 和 max_value 需要返回 -1

示例 1：

输入: 
["MaxQueue","push_back","push_back","max_value","pop_front","max_value"]
[[],[1],[2],[],[],[]]
输出: [null,null,null,2,1,2]
示例 2：

输入: 
["MaxQueue","pop_front","max_value"]
[[],[],[]]
输出: [null,-1,-1]
 

限制：

1 <= push_back,pop_front,max_value的总操作数 <= 10000
1 <= value <= 10^5

 

解题思路：

本质上是再类里面维护一个辅助队列，辅助队列维护最大值的滑动窗口。

1.正常队列。用于满足出队，入队操作。

1.辅助队列，队首永远是最大值。（存储队列各个数的地址）

 

#include 
#include 
#include 
using namespace std;
class MaxQueue {
public:
	MaxQueue() {
	}

	int max_value() {
		if (m_deque.empty()) {
			return -1;
		}
		else {			
			return (*m_assist.front());
		}
	}

	void push_back(int value) {

		m_deque.push_back(value);

		while (!m_assist.empty() && (*m_assist.back()) < value)
			m_assist.pop_back();
		m_assist.push_back(m_deque.end()-1);
	}

	int pop_front() {

		if (m_deque.empty()) {
			return -1;
		}
		else {
			int front = m_deque.front();
			if (m_assist.front() == m_deque.begin()) {
				m_assist.pop_front();
			}
			m_deque.pop_front();
			return front;
		}
	}

private:
	deque m_deque;                     /* 正常队列 */
	deque::iterator> m_assist;   /* 辅助队列 */
};

/**
 * Your MaxQueue object will be instantiated and called as such:
 * MaxQueue* obj = new MaxQueue();
 * int param_1 = obj->max_value();
 * obj->push_back(value);
 * int param_3 = obj->pop_front();
 */

int main() {

	//["MaxQueue", "pop_front", "pop_front", "pop_front", "pop_front", "pop_front", "push_back", "max_value", "push_back", "max_value"]
	// [[], [], [], [], [], [], [15], [], [9], []]

	//["MaxQueue", "push_back", "push_back", "max_value", "pop_front", "max_value"]
	//[[], [1], [2], [], [], []]

	//["MaxQueue", "max_value", "pop_front", "pop_front", "push_back", "push_back", "push_back", "pop_front", "push_back", "pop_front"]
	//[[], [], [], [], [94], [16], [89], [], [22], []]

	//MaxQueue* pm = new MaxQueue();
	//cout << pm->pop_front() << endl;
	//cout << pm->pop_front() << endl;
	//cout << pm->pop_front() << endl;
	//cout << pm->pop_front() << endl;
	//cout << pm->pop_front() << endl;
	//pm->push_back(15);
	//cout << pm->max_value() << endl;
	//pm->push_back(9);
	//cout << pm->max_value() << endl;


	//MaxQueue* pm = new MaxQueue();
	//pm->push_back(1);
	//pm->push_back(2);
	//cout << pm->max_value() << endl;
	//cout << pm->pop_front() << endl;
	//cout << pm->max_value() << endl;


	MaxQueue* pm = new MaxQueue();
	cout << pm->max_value() << endl;
	cout << pm->pop_front() << endl;
	cout << pm->pop_front() << endl;
	pm->push_back(94);
	pm->push_back(16);
	pm->push_back(89);
	cout << pm->pop_front() << endl;
	pm->push_back(22);
	cout << pm->pop_front() << endl;

	return 0;
}