题目
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
解题记录
- 一个栈中存放append的数据
- 另一个栈中存放将要pop出颠倒顺序后的数据
import java.util.Deque;
import java.util.LinkedList;
/**
* @author ffzs
* @describe
* @date 2020/6/30
*/
public class CQueue {
Deque<Integer> s1;
Deque<Integer> s2;
public CQueue() {
s1 = new LinkedList<>();
s2 = new LinkedList<>();
}
public void appendTail(int value) {
s1.push(value);
}
public int deleteHead() {
if (!s2.isEmpty()) return s2.pop();
while (!s1.isEmpty()) s2.push(s1.pop());
if (!s2.isEmpty()) return s2.pop();
else return -1;
}
}