Leetcode Implement Queue using Stacks

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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).

题目意思：

　　用栈实现队列

解题思路：

　　用两个栈实现，一个栈用作队列的出口，一个栈用作队列的进口

扩展：

　　c++ 的STL中队列的实现不是用的栈，其实现原理是开辟一段内存，该内存中每个节点指向一段连续的内存空间，然后维护这些结点，具体参考《STL源码剖析》，面试时可能会问到STL队列的实现方式。STL中还有个优先权队列，其实现原理是用的堆数据结构实现的，堆排序算法最好自己能写。

源代码：

 1 class Queue{
 2     stack<int> inStack, outStack;
 3 public:
 4     void  push(int x){
 5         inStack.push(x);
 6     }
 7     void pop(void){
 8         if(outStack.empty()){
 9             while(!inStack.empty()){
10                 outStack.push(inStack.top());
11                 inStack.pop();
12             }
13         }
14         outStack.pop();
15     }
16 
17     int peek(void){
18         if(outStack.empty()){
19             while(!inStack.empty()){
20                 outStack.push(inStack.top());
21                 inStack.pop();
22             }
23         }
24         return outStack.top();
25     }
26 
27     bool empty(void) {
28         return inStack.empty() && outStack.empty();
29     }
30 };

Leetcode Implement Queue using Stacks

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原文地址：http://www.cnblogs.com/xiongqiangcs/p/4627301.html