Problem: 232. 用栈实现队列

题目描述

思路

利用两个栈，一个入栈一个出栈搭配着实现队列的相关操作：

1.创建两个栈stack1和stack2；
2.void push(int x):将要入队的元素先入栈stack1；
3.int pop()：当stack2为空时并且stack1不为空时将stack1中的元素均弹出并同时依次入栈stack2，最后将stack2的栈顶元素弹出
4.int peek()：同理pop；
5.boolean empty():只用两个栈均为空时才返回true

Code

class MyQueue {private Stack<Integer> stack1;private Stack<Integer> stack2;public MyQueue() {stack1 = new Stack<>();stack2 = new Stack<>();}/*** Push the element to the stack1** @param x The element to be pushed*/public void push(int x) {stack1.push(x);}/*** Pop the top element of stack2** @return int*/public int pop() {if (stack2.isEmpty()) {while (!stack1.isEmpty()) {stack2.push(stack1.pop());}}return stack2.pop();}/*** Peek the top element of stack2** @return int*/public int peek() {if (stack2.isEmpty()) {if (stack2.isEmpty()) {while (!stack1.isEmpty()) {stack2.push(stack1.pop());}}}return stack2.peek();}/*** Check the empty of myQueue** @return boolean*/public boolean empty() {if (stack1.empty() && stack2.isEmpty()) {return true;}return false;}
}
/*** Your MyQueue object will be instantiated and called as such:* MyQueue obj = new MyQueue();* obj.push(x);* int param_2 = obj.pop();* int param_3 = obj.peek();* boolean param_4 = obj.empty();*/