The queue achieves max operations, and the efficiency should be improved as much as possible.

Combine the previously implemented maxstack and use two stacks to implement one queue to implement maxqueue

 

import java.util.Stack;public class MaxQueue {    MaxStack in = new MaxStack();    MaxStack out = new MaxStack();    public void enqueue(Integer a) {        in.push(a);    }    public Integer dequeue() {        shiftItems();        return out.pop();    }    public Integer peek() {        shiftItems();        return out.peek();    }    public Integer max() {        return Math.max(in.isEmpty() ? Integer.MIN_VALUE : in.max(), out.isEmpty() ? Integer.MIN_VALUE : out.max());    }    private void shiftItems() {        if (!out.isEmpty())            return;        while (!in.isEmpty()) {            out.push(in.pop());        }    }    public static void main(String[] args) {        MaxQueue queue = new MaxQueue();        queue.enqueue(1);        System.out.println(queue.max());        queue.enqueue(2);        System.out.println(queue.max());        queue.enqueue(3);        System.out.println(queue.max());        queue.enqueue(4);        System.out.println(queue.max());        queue.dequeue();        System.out.println(queue.max());        queue.dequeue();        System.out.println(queue.max());        queue.dequeue();        System.out.println(queue.max());    }}class MaxStack {    Stack<Integer> val = new Stack<Integer>();    Stack<Integer> max = new Stack<Integer>();    public boolean isEmpty() {        return val.isEmpty();    }    public void push(Integer a) {        val.push(a);        if (max.isEmpty() || a >= max.peek())            max.push(a);    }    public Integer pop() {        Integer out = val.pop();        if (out == max.peek())            max.pop();        return out;    }    public Integer peek() {        return val.peek();    }    public Integer max() {        return max.peek();    }}