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
     
       stack1=new Stack
      
       (); 4     Stack
       
         stack2=new Stack
        
         (); 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  */