【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

 1 public class MyQueue {
 2 
 3    Stack<Integer> stack1=new Stack<Integer>();
 4     Stack<Integer> stack2=new Stack<Integer>();
 5     
 6     /** Push element x to the back of queue. */
 7     public void push(int x) {
 8         stack1.push(x);
 9     }
10     
11     /** Removes the element from in front of queue and returns that element. */
12     public int pop() {
13         if(!stack2.isEmpty())
14             return stack2.pop();
15         else{
16             while(!stack1.empty())
17                 stack2.push(stack1.pop());
18             return stack2.pop();
19         }
20     }
21     
22     /** Get the front element. */
23     public int peek() {
24         if(!stack2.isEmpty())
25             return stack2.peek();
26         else{
27             while(!stack1.empty())
28                 stack2.push(stack1.pop());
29             return stack2.peek();
30         }
31     }
32     
33     /** Returns whether the queue is empty. */
34     public boolean empty() {
35         return stack1.empty()&&stack2.empty();
36     }
37 }
38 
39 /**
40  * Your MyQueue object will be instantiated and called as such:
41  * MyQueue obj = new MyQueue();
42  * obj.push(x);
43  * int param_2 = obj.pop();
44  * int param_3 = obj.peek();
45  * boolean param_4 = obj.empty();
46  */