【LeetCode232】 Implement Queue using Stacks★

1.题目描述

2.思路

　　思路简单，这里用一个图来举例说明：

3.java代码

 public class MyQueue {

    Stack<Integer> stack1=new Stack<Integer>();
     Stack<Integer> stack2=new Stack<Integer>();

     /** Push element x to the back of queue. */
     public void push(int x) {
         stack1.push(x);
     }

     /** Removes the element from in front of queue and returns that element. */
     public int pop() {
         if(!stack2.isEmpty())
             return stack2.pop();
         else{
             while(!stack1.empty())
                 stack2.push(stack1.pop());
             return stack2.pop();
         }
     }

     /** Get the front element. */
     public int peek() {
         if(!stack2.isEmpty())
             return stack2.peek();
         else{
             while(!stack1.empty())
                 stack2.push(stack1.pop());
             return stack2.peek();
         }
     }

     /** Returns whether the queue is empty. */
     public boolean empty() {
         return stack1.empty()&&stack2.empty();
     }
 }

 /**
  * 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();
  */