DailyChallenge
剑指 Offer 09. 用两个栈实现队列
Easy20200630
Description
用两个栈实现一个队列。队列的声明如下，请实现它的两个函数 appendTail 和 deleteHead ，分别完成在队列尾部插入整数和在队列头部删除整数的功能。(若队列中没有元素，deleteHead 操作返回 -1 )
示例 1：输入：
["CQueue","appendTail","deleteHead","deleteHead"]
[[],[3],[],[]]
输出：[null,null,3,-1]示例 2：输入：
["CQueue","deleteHead","appendTail","appendTail","deleteHead","deleteHead"]
[[],[],[5],[2],[],[]]
输出：[null,-1,null,null,5,2]提示：
- 1 <= values <= 10000
- 最多会对 appendTail、deleteHead 进行 10000 次调用
链接：
https://leetcode-cn.com/problems/yong-liang-ge-zhan-shi-xian-dui-lie-lcof
Solution
注意 stack 不要用stack，要用deque。
class CQueue {Deque<Integer> stack1;Deque<Integer> stack2;public CQueue() {stack1 = new LinkedList<>();stack2 = new LinkedList<>();}public void appendTail(int value) {stack1.add(value);}public int deleteHead() {if(stack2.isEmpty()){while(!stack1.isEmpty()){stack2.add(stack1.pop());}}return stack2.isEmpty()? -1 : stack2.pop();}
}/*** Your CQueue object will be instantiated and called as such:* CQueue obj = new CQueue();* obj.appendTail(value);* int param_2 = obj.deleteHead();*/
