面试题 03.04. 化栈为队

 1 class MyQueue {
 2 public:
 3     stack<int> que;
 4     stack<int> temp;
 5     /** Initialize your data structure here. */
 6     MyQueue() 
 7     {
 8     }
 9     
10     /** Push element x to the back of queue. */
11     void push(int x) 
12     {
13         que.push(x);
14     }
15     
16     /** Removes the element from in front of queue and returns that element. */
17     int pop() 
18     {
19         if(!temp.empty())
20         {
21             int value = temp.top();
22             temp.pop();
23             return value;
24         }
25         else
26         {
27             while(!que.empty())
28             {
29                 temp.push(que.top());
30                 que.pop();
31             }
32             int value = temp.top();
33             temp.pop();
34             return value;
35         }
36     }
37     
38     /** Get the front element. */
39     int peek() 
40     {
41         if(!temp.empty())
42         {
43             return temp.top();
44         }
45         else
46         {
47             while(!que.empty())
48             {
49                 temp.push(que.top());
50                 que.pop();
51             }
52             return temp.top();
53         }
54     }
55     
56     /** Returns whether the queue is empty. */
57     bool empty() 
58     {
59         return que.empty() && temp.empty();
60     }
61 };
62 
63 /**
64  * Your MyQueue object will be instantiated and called as such:
65  * MyQueue* obj = new MyQueue();
66  * obj->push(x);
67  * int param_2 = obj->pop();
68  * int param_3 = obj->peek();
69  * bool param_4 = obj->empty();
70  */