The sword refers to the maximum value of the Offer-65 queue

// Storage queue 
Queue<Integer> queue; 
// Monotonic two-way queue 
Deque<Integer> deque; 

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

public int max_value() { 
    // empty return -1 non-empty return head of the queue 
    return deque.isEmpty()? -1: deque.peekFirst(); 
} 

public void push_back(int value) { 
    queue.offer(value); 
    // delete in a loop until The values ​​in the queue are greater than the current value, or the queue is empty 
    while(!deque.isEmpty() && deque.peekLast() <value){ 
        // When the queue is not empty, the current value is compared with the value at the end of the queue, if Is greater than, delete the tail value of the queue 
        deque.removeLast(); 
    } 
    // After executing the above loop, the queue is either empty or the value is greater than the current value, and then the current value is added to the queue 
    deque.offerLast(value ); 
}

public int pop_front() { 
    // Empty return -1 
    if (queue.isEmpty()){ 
        return -1; 
    } 
    // If the head of the data queue and the monotonic two-way queue are equal 
    if (queue.peek().equals(deque. peekFirst())){ 
        // Monotonic two-way queues should also be popped to keep the elements of the two queues consistent 
        deque.removeFirst(); 
    } 
    return queue.remove(); 
} 

public static void main(String[] args) { 
    MaxQueue65 obj = new MaxQueue65(); 
    obj.push_back(1); 
    obj.push_back(2); 
    System.out.println(obj.max_value()); 
    System.out.println(obj.pop_front()); 
    System.out.println (obj.max_value()); 
}