剑指 Offer 09. 用两个栈实现队列

题目：

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

代码：

/**
 * Your CQueue object will be instantiated and called as such:
 * CQueue obj = new CQueue();
 * obj.appendTail(value);
 * int param_2 = obj.deleteHead();
 */
 
class CQueue {
    private int head;
    private int tail;
    int[] ob;
    public CQueue() {
        this.head=0;
        this.tail=0;  //初始头尾在一个下标
        this.ob=new int[10000];
    }

    public void appendTail(int value) {
        this.ob[this.tail++]=value;
    }
    
    public int deleteHead() {
        if(this.head==this.tail){return -1;}
        return this.ob[this.head++];
    }
}