Implement Queue using Stacks问题及解法

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问题描述：

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).

问题分析：

用栈来实现队列，过程要注意队列和栈各自的性质：队列FIFO，栈FILO。

过程详见代码：

class MyQueue {
public:stack<int> t;/** Initialize your data structure here. */MyQueue() {}/** Push element x to the back of queue. */void push(int x) {stack<int> s;while(!t.empty()){s.push(t.top());t.pop();}s.push(x);while(!s.empty()){t.push(s.top());s.pop();}}/** Removes the element from in front of queue and returns that element. */int pop() {int res = t.top();t.pop();return res;   }/** Get the front element. */int peek() {return t.top();}/** Returns whether the queue is empty. */bool empty() {return t.empty();}
};

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