剑指offer--面试题7: 用两个栈实现队列



题目描述

用两个栈来实现一个队列，完成队列的Push和Pop操作。 队列中的元素为int类型。

python实现：

# -*- coding:utf-8 -*-
class Solution:
    def __init__(self):
        self.stack1 = []#入队操作
        self.stack2 = []#
    def push(self, node):
        # write code here
        """
        总往stack1里入队
        """
        self.stack1.append(node)
         
    def pop(self):
        # return xx
        """
        stack2里不为空，就直接弹出即为结果，否则将stack1里的元素全部移到stack2，直至
        stack1里只剩下一个，弹出即为结果
        """
        if self.stack2:
            return self.stack2.pop()
        if len(self.stack1)==0:
            raise Exception("pop error since queue is empty")
        while len(self.stack1)>1:
            self.stack2.append(self.stack1.pop())
        return self.stack1.pop()

c++实现：

class Solution
{
public:
    void push(int node) {
        stack1.push(node);
    }
 
    int pop() {
        int result;
        if(stack2.size()>0){
            result = stack2.top();
            stack2.pop();
            return result;
        }
        //if(stack1.size()==0)
        //    throw new exception("queue is empty");
        int tmp;
        while(stack1.size()>1){
            tmp = stack1.top();
            stack1.pop();
            stack2.push(tmp);
        }
        result = stack1.top();
        stack1.pop();
         return result;   
    }
 
private:
    stack<int> stack1;
    stack<int> stack2;
};