用两个栈实现队列

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],[],[]]

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输出：[null,null,3,-1]

var CQueue = function() {
    this.stack1 = []
    this.stack2 = []
    this.size = 0
};

/** 
 * @param {number} value
 * @return {void}
 */
CQueue.prototype.appendTail = function(value) {
    this.stack1.push(value)
    this.size++
};

/**
 * @return {number}
 */
CQueue.prototype.deleteHead = function() {
    if(this.size === 0) return -1

    if(!this.stack2.length) {
        while(this.stack1.length) {
            this.stack2.push(this.stack1.pop())
        }
    }

    this.size--
    return this.stack2.pop()
};

/**
 * Your CQueue object will be instantiated and called as such:
 * var obj = new CQueue()
 * obj.appendTail(value)
 * var param_2 = obj.deleteHead()
 */

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来源：力扣（LeetCode）链接：https://leetcode-cn.com/problems/yong-liang-ge-zhan-shi-xian-dui-lie-lcof

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