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]
class CQueue { public: stack<int>stack1; stack<int>stack2; CQueue() { } void appendTail(int value) { stack1.push(value); } int deleteHead() { if(stack1.empty()) return -1; while(!stack1.empty()){ stack2.push(stack1.top()); stack1.pop(); } int res = stack2.top(); stack2.pop(); while(!stack2.empty()){ stack1.push(stack2.top()); stack2.pop(); } return res; } };
