LeetCode:Implement Queue using Stacks

Implement the following operations of a queue using stacks.

  • push(x) -- Push element x to the back of queue.
  • pop() -- Removes the element from in front of queue.
  • peek() -- Get the front element.
  • empty() -- Return whether the queue is empty.

Notes:

  • You must use only standard operations of a stack -- which means only push to top, peek/pop from top, size, and is empty operations are valid.
  • Depending on your language, stack may not be supported natively. You may simulate a stack by using a list or deque (double-ended queue), as long as you use only standard operations of a stack.
  • You may assume that all operations are valid (for example, no pop or peek operations will be called on an empty queue).
 
 两个栈实现队列。
 1 class Queue {
 2 private:
 3     stack<int> stack1,stack2;
 4 public:
 5     // Push element x to the back of queue.
 6     void push(int x) {
 7       
 8         stack1.push(x);
 9         
10     }
11 
12     // Removes the element from in front of queue.
13     void pop(void) {
14         if(stack2.empty())
15         {
16             while(!stack1.empty())
17             {
18                 stack2.push(stack1.top());
19                 stack1.pop();
20             }
21         }
22         stack2.pop();
23         
24     }
25 
26     // Get the front element.
27     int peek(void) {
28         if(stack2.empty())
29         {
30             while(!stack1.empty())
31             {
32                 stack2.push(stack1.top());
33                 stack1.pop();
34             }
35         }
36         return stack2.top();
37         
38         
39     }
40 
41     // Return whether the queue is empty.
42     bool empty(void) {
43         if(stack1.empty()&&stack2.empty())
44             return true;
45         else
46             return false;
47         
48     }
49 };

 

posted @ 2015-08-12 10:48  尾巴草  阅读(128)  评论(0)  编辑  收藏  举报