#yyds干货盘点# LeetCode程序员面试金典：化栈为队

题目：

实现一个MyQueue类，该类用两个栈来实现一个队列。

示例：

MyQueue queue = new MyQueue();

queue.push(1);

queue.push(2);

queue.peek();  // 返回 1

queue.pop();   // 返回 1

queue.empty(); // 返回 false

代码实现：

class MyQueue { Deque<Integer> inStack; Deque<Integer> outStack; public MyQueue() { inStack = new ArrayDeque<Integer>(); outStack = new ArrayDeque<Integer>(); } public void push(int x) { inStack.push(x); } public int pop() { if (outStack.isEmpty()) { in2out(); } return outStack.pop(); } public int peek() { if (outStack.isEmpty()) { in2out(); } return outStack.peek(); } public boolean empty() { return inStack.isEmpty() && outStack.isEmpty(); } private void in2out() { while (!inStack.isEmpty()) { outStack.push(inStack.pop()); } }}