[offer9] implement queues with two stacks

subject

Use two stacks to implement a queue . The declaration of the queue is as follows , Please implement its two functions appendTail and deleteHead , The functions of inserting integers at the end of the queue and deleting integers at the head of the queue are respectively completed .( If there are no elements in the queue ,deleteHead Operation return -1 )

Input ：
[“CQueue”,“appendTail”,“deleteHead”,“deleteHead”]
[[],[3],[],[]]
Output ：[null,null,3,-1]
// explain ： Entering . The brackets above are operations . The following brackets are the data of the operation .

source ： Power button （LeetCode）
link ：https://leetcode.cn/problems/yong-liang-ge-zhan-shi-xian-dui-lie-lcof
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class CQueue {
    
    private Stack<Integer> in;// Specially for joining the team 
    private Stack<Integer> out;// Out of the team 
    public CQueue() {
    
        in=new Stack<>();
        out=new Stack<>();
    }

    public void appendTail(int value) {
    
        in.push(value);
    }

    public int deleteHead() {
    
        if(!out.empty()){
    
            return out.pop();
        }else{
    
            while(!in.empty()){
    
                out.push(in.pop());
            }
            return out.isEmpty()?-1:out.pop();
        }
    }
}