剑指Offer 09 用两个栈实现队列

用两个栈实现队列

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。

# -*- coding:utf-8 -*-
class Solution:
    def __init__(self):
        self.list1 = []
        self.list2 = []
        
    def push(self, node):
        self.list1.append(node)
        # write code here
    def pop(self):
        if len(self.list2) == 0:
            while len(self.list1) > 1:
                top = self.list1.pop(-1)
                self.list2.append(top)
            return self.list1.pop(-1)
        return self.list2.pop(-1)
        # return xx

 

leetcode地址，Java版代码：

class CQueue {
    Stack<Integer> S1;
    Stack<Integer> S2;
    public CQueue() {
        S1 = new Stack<Integer>();
        S2 = new Stack<Integer>();
    }
    public void appendTail(int value) {
        S1.push(value);
    }        
    public int deleteHead() {
        if(S2.isEmpty()) {
            while(!S1.isEmpty()) {
                int top = S1.pop();
                S2.push(top);
            }
        }
        if(!S2.isEmpty()){
            int cur = S2.pop();
            return cur;
        }
        return -1;
    }
}