【剑指Offer】59.2 队列的最大值

class MaxQueue {
    Queue<Integer> que;
    Deque<Integer> deq; // 记录最大值

    public MaxQueue() {
        que = new LinkedList<>();
        deq = new LinkedList<>();
    }
    
    public int max_value() {
        // 取dep的队首为最大值
        return deq.size() > 0 ? deq.peek() : -1;
    }
    
    public void push_back(int value) {
        que.add(value);
        while(deq.size() > 0 && deq.peekLast() < value) // 从队尾删除小于value的元素，保留队列最大值
            deq.pollLast();
        deq.add(value);
    }
    
    public int pop_front() {
        int v = que.size() > 0 ? que.poll() : -1;
        if(deq.size() > 0 && deq.peekFirst() == v)
            deq.pollFirst();
        return v;
    }
}

/**
 * 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();
 */