232. Implement Queue using Stacks

 1 class MyQueue 
 2 {
 3 private: 
 4     stack<int> st;
 5 public:
 6     /** Initialize your data structure here. */
 7     MyQueue() {
 8         
 9     }
10     
11     /** Push element x to the back of queue. */
12     void push(int x) 
13     {
14         stack<int> cur;
15         if(!st.empty())
16             while(!st.empty())
17             {
18                 int i=st.top();
19                 cur.push(i);
20                 st.pop();
21             }
22         cur.push(x);
23         while(!cur.empty())
24         {
25             int j=cur.top();
26             st.push(j);
27             cur.pop();
28         }
29     }
30     
31     /** Removes the element from in front of queue and returns that element. */
32     int pop() 
33     {
34         int i=st.top();
35         st.pop();
36         return i;
37     }
38     
39     /** Get the front element. */
40     int peek() 
41     {
42         return st.top();
43     }
44     
45     /** Returns whether the queue is empty. */
46     bool empty() 
47     {
48         return st.empty();
49     }
50 };
51 
52 /**
53  * Your MyQueue object will be instantiated and called as such:
54  * MyQueue obj = new MyQueue();
55  * obj.push(x);
56  * int param_2 = obj.pop();
57  * int param_3 = obj.peek();
58  * bool param_4 = obj.empty();
59  */

用栈模拟队列，俩栈倒过来倒过去的，完事儿