Realize queue with stack based on java

topic description

Please use only two stacks to implement a first-in-first-out queue. The queue should support all operations supported by general queues (push, pop, peek, empty):

Implement the MyQueue class:

void push(int x) 将元素 x 推到队列的末尾
int pop() 从队列的开头移除并返回元素
int peek() 返回队列开头的元素
boolean empty() 如果队列为空，返回 true ；否则，返回 false

Note:
You can only use standard stack operations—that is, only push to top, peek/pop from top, size, and is empty operations are legal.
Your language may not support stacks. You can use list or deque (double-ended queue) to simulate a stack, as long as it is a standard stack operation.

example

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answer

import javautil.Stack;
class  MyQueue {
    
    

        Stack<Integer>  stack1;
        Stack<Integer>  stack2;

        public MyQueue() {
    
    
            stack1 = new Stack<>();
            stack2 = new Stack<>();
        }

        public void push(int x) {
    
    
            stack1.push(x);
        }

        public int pop() {
    
    
            if(empty()){
    
    
                return -1;
            }
            if(stack2.isEmpty()){
    
    
                while(!stack1.isEmpty()){
    
    
                    int ret = stack1.pop();
                    stack2.push(ret);
                }
            }
            return stack2.pop();
        }

        public int peek() {
    
    
            if(empty()){
    
    
                return -1;
            }
            if(stack2.isEmpty()){
    
    
                while(!stack1.isEmpty()){
    
    
                    int ret = stack1.pop();
                    stack2.push(ret);
                }
            }
            return stack2.peek();
        }

        public boolean empty() {
    
    
            if(stack1.isEmpty() && stack2.isEmpty()){
    
    
                return true;
            }
            return false;
        }
    }

Result (with test)

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