一、题目链接

用栈实现队列

二、解题思路

三、解题代码

class MyQueue {

    public Stack<Integer> stack1 ;
    public 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.empty()){
            return stack2.pop();
        }else{
            int curSize = stack1.size();
            while(curSize != 0){
                stack2.push(stack1.pop());
                curSize--;
            }
            return stack2.pop();
        }
    }

    public int peek() {
        if (empty()){
            return -1;
        }
        if(!stack2.empty()){
            return stack2.peek();
        }else{
            int curSize = stack1.size();
            while(curSize != 0){
                stack2.push(stack1.pop());
                curSize--;
            }
            return stack2.peek();
        }
    }

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