Implement the following operations of a stack using queues.
push(x) -- Push element x onto stack.
pop() -- Removes the element on top of the stack.
top() -- Get the top element.
empty() -- Return whether the stack is empty.
Notes
You must use only standard operations of a queue -- which means only push to back, peek/pop from front, size, and is empty operations are valid.
Depending on your language, queue may not be supported natively. You may simulate a queue by using a list or deque (double-ended queue), as long as you use only standard operations of a queue.
You may assume that all operations are valid (for example, no pop or top operations will be called on an empty stack).
题目的意思是让我们用队列的基本操作来完成栈的操作，你可以再借助一个队列或者双向链表。
你能使用的队列的方法只有push，pop（这个方法在队列中是从队头去除元素，而不是队尾），peek（在C++中是front方法），size和empty
很简单的题目，学过数据结构的应该都能实现
class Stack { public: queue<int> que1, que2; // Push element x onto stack. void push(int x) { que1.push(x); } // Removes the element on top of the stack. void pop() { int i = 1,elem=0; while (i<que1.size()) { elem = que1.front(); que2.push(elem); que1.pop(); } que1.pop(); while (!que2.empty()) { elem = que2.front(); que1.push(elem); que2.pop(); } } // Get the top element. int top() { int i = 1, elem = 0; while (i<que1.size()) { elem = que1.front(); que2.push(elem); que1.pop(); } i = que1.front(); que2.push(i); que1.pop(); while (!que2.empty()) { elem = que2.front(); que1.push(elem); que2.pop(); } return i; } // Return whether the stack is empty. bool empty() { return que1.empty(); } };
LeetCode Implement Stack using Queues
原文：http://www.cnblogs.com/csudanli/p/5335509.html