DAY 47 leetcode 232--栈与队列.用栈实现队列

题号232

请你仅使用两个栈实现先入先出队列。队列应当支持一般队列支持的所有操作（push、pop、peek、empty）：

class MyQueue {Stack<Integer> stackIn;Stack<Integer> stackOut;/** Initialize your data structure here. */public MyQueue() {stackIn = new Stack<>(); // 负责进栈stackOut = new Stack<>(); // 负责出栈}/** Push element x to the back of queue. */public void push(int x) {stackIn.push(x);}/** Removes the element from in front of queue and returns that element. */public int pop() {    dumpstackIn();return stackOut.pop();}/** Get the front element. */public int peek() {dumpstackIn();return stackOut.peek();}/** Returns whether the queue is empty. */public boolean empty() {return stackIn.isEmpty() && stackOut.isEmpty();}// 如果stackOut为空，那么将stackIn中的元素全部放到stackOut中private void dumpstackIn(){if (!stackOut.isEmpty()) return; while (!stackIn.isEmpty()){stackOut.push(stackIn.pop());}}
}