题目链接:https://leetcode-cn.com/problems/yong-liang-ge-zhan-shi-xian-dui-lie-lcof/
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]
思路
用两个栈来分别实现删头和加尾的操作;
删头时,如果两个栈都为空,说明队列中没有数;如果尾部栈不为空,将尾部栈转入头部栈中,pop掉第一个;
加尾时,如果头部栈不为空 ,将头部栈转入尾部栈,在最后加入新的value
class CQueue {
stack<int> head;
stack<int> tail;
public:
CQueue() {
}
void appendTail(int value) {
while(!head.empty()){
tail.push(head.top());
head.pop();
}
tail.push(value);
}
int deleteHead() {
if(tail.empty()&&head.empty())
return -1;
while(!tail.empty()){
head.push(tail.top());
tail.pop();
}
int temp= head.top();
head.pop();
return temp;
}
};
/**
* Your CQueue object will be instantiated and called as such:
* CQueue* obj = new CQueue();
* obj->appendTail(value);
* int param_2 = obj->deleteHead();
*/