题目描述

示例1

示例2

做题思路

代码

class MaxQueue {
    Queue<Integer> queue;//普通队列
    Deque<Integer> deque;//递减双端队列
    public MaxQueue() {
        queue = new LinkedList<>();//队列初始化
        deque = new LinkedList<>();//双端队列初始化
    }
    public int max_value() {
        return deque.isEmpty() ? -1 : deque.peekFirst();//若队列为空返回-1，否则返回deque左顶端元素
    }
    public void push_back(int value) {
        queue.offer(value);//元素入队
        while(!deque.isEmpty() && deque.peekLast() < value)
            deque.pollLast();//如果deque非空且右顶端元素小于value则出队
        deque.offerLast(value);//value入deque右端，保持deque递减
    }
    public int pop_front() {
        if(queue.isEmpty()) return -1;
        if(queue.peek().equals(deque.peekFirst()))
            deque.pollFirst();//如果deque左顶端元素等于queue出队元素，则弹出deque左顶端元素
        return queue.poll();
    }
}

/**
 * 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();
 */