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
思路:
把2个栈的栈底连起来,就像2个杯子合起来,中间打穿就变成了一根管子
class CQueue {
public:
CQueue() {
}
void appendTail(int value) {
s1.push(value);
}
int deleteHead() {
int ans;
if(s2.size())
{
ans=s2.top();
s2.pop();
return ans;
}
if(!s1.size())return -1;
while(s1.size())
{
s2.push(s1.top());
s1.pop();
}
return deleteHead();
}
private:
stack<int>s1,s2;
};