[LintCode] 用栈实现队列

 1 class Queue {
 2 public:
 3     stack<int> stack1;
 4     stack<int> stack2;
 5
 6     Queue() {
 7         // do intialization if necessary
 8     }
 9
10     void push(int element) {
11         // write your code here
12         stack1.push(element);
13     }
14
15     int pop() {
16         // write your code here
17         if (stack2.empty()) {
18             while (!stack1.empty()) {
19                 int elem = stack1.top();
20                 stack1.pop();
21                 stack2.push(elem);
22             }
23         }
24         int elem = stack2.top();
25         stack2.pop();
26         return elem;
27     }
28
29     int top() {
30         // write your code here
31         if (stack2.empty()) {
32             while (!stack1.empty()) {
33                 int elem = stack1.top();
34                 stack1.pop();
35                 stack2.push(elem);
36             }
37         }
38         return stack2.top();
39     }
40 };