剑指 Offer 59 - II. 队列的最大值

public class MaxQueue {

    private final Queue<Integer> queue;
    private final Deque<Integer> deque; // 非严格递减队列

    public MaxQueue() {
        this.queue = new LinkedList<>();
        this.deque = new LinkedList<>();
    }

    public int max_value() {
        if (deque.isEmpty()) {
            return -1;
        } else {
            return deque.peekFirst();
        }
    }

    public void push_back(int value) {
        queue.offer(value);

        while (!deque.isEmpty() && value >= deque.peekLast()) {
            deque.pollLast();
        }
        deque.offerLast(value);
    }

    public int pop_front() {
        if (queue.isEmpty()) {
            return -1;
        } else {
            int value = queue.poll();
            if (value == deque.peekFirst()) {
                deque.pollFirst();
            }
            return value;
        }
    }

}
Reference
