剑指 Offer 09. 用两个栈实现队列

题目描述：

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]

 1 class CQueue {
 2     Deque<Integer> stack1;
 3     Deque<Integer> stack2;
 4     
 5     public CQueue() {
 6         stack1 = new LinkedList<Integer>();
 7         stack2 = new LinkedList<Integer>();
 8     }
 9     
10     public void appendTail(int value) {
11         stack1.push(value);
12 
13     }
14     
15     public int deleteHead() {
16         if(stack2.isEmpty()){
17           if(stack1.isEmpty()){
18               return -1;
19           }
20          while(!stack1.isEmpty()){
21                stack2.push(stack1.pop());
22            }
23 
24 
25         }
26         return stack2.pop();
27 
28     }
29 }
30 
31 /**
32  * Your CQueue object will be instantiated and called as such:
33  * CQueue obj = new CQueue();
34  * obj.appendTail(value);
35  * int param_2 = obj.deleteHead();
36  */

 

posted on 2021-03-26 14:38  wxcongajiayou  阅读(31)  评论(0)    收藏  举报