import java.util.Stack;
/**
*
使用栈实现队列的下列操作：
push(x) -- 将一个元素放入队列的尾部。
pop() -- 从队列首部移除元素。
peek() -- 返回队列首部的元素。
empty() -- 返回队列是否为空。
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
https://leetcode-cn.com/problems/implement-queue-using-stacks/
*/
class MyQueue {
Stack<Integer> numStack;//数值栈
Stack<Integer> queueStack;//队列栈
/** Initialize your data structure here. */
public MyQueue() {
numStack = new Stack<>();
queueStack = new Stack<>();
}
/** Push element x to the back of queue. */
public void push(int x) {
while (!queueStack.isEmpty()){
numStack.push(queueStack.pop());
}
numStack.push(x);
}
/** Removes the element from in front of queue and returns that element. */
public int pop() {
while (!numStack.isEmpty()){
queueStack.push(numStack.pop());
}
return queueStack.pop();
}
/** Get the front element. */
public int peek() {
while (!numStack.isEmpty()){
queueStack.push(numStack.pop());
}
return queueStack.peek();
}
/** Returns whether the queue is empty. */
public boolean empty() {
while (!numStack.isEmpty()){
queueStack.push(numStack.pop());
}
return queueStack.isEmpty();
}
public static void main(String[] args){
MyQueue queue = new MyQueue();
queue.push(1);
queue.push(2);
System.out.println(queue.peek());// 返回 1
System.out.println(queue.pop());// 返回 1
System.out.println(queue.empty());// 返回 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();
*/
