232. 用栈实现队列

peek()中！！！this.pop()

var MyQueue = function() {
    this.stackIn = [];
    this.stackOut = [];

};

/** 
 * @param {number} x
 * @return {void}
 */
MyQueue.prototype.push = function(x) {
    this.stackIn.push(x);
};

/**
 * @return {number}
 */
//  重点是弹出的规则
MyQueue.prototype.pop = function() {
    const size = this.stackOut.length;
    if (size) {
        return this.stackOut.pop();
    }

    while(this.stackIn.length) {
        this.stackOut.push(this.stackIn.pop());
    }
    return this.stackOut.pop();
};

/**
 * @return {number}
 */
MyQueue.prototype.peek = function() {
    // 这里真害人
    let res = this.pop();
    this.stackOut.push(res);
    return res;
};

/**
 * @return {boolean}
 */
MyQueue.prototype.empty = function() {
    return !this.stackIn.length && !this.stackOut.length
};

/**
 * Your MyQueue object will be instantiated and called as such:
 * var obj = new MyQueue()
 * obj.push(x)
 * var param_2 = obj.pop()
 * var param_3 = obj.peek()
 * var param_4 = obj.empty()
 */

225. 用队列实现栈

单队列实现

// 单队列实现
var MyStack = function() {
    this.queue = [];
};

/** 
 * @param {number} x
 * @return {void}
 */
MyStack.prototype.push = function(x) {
    this.queue.push(x);
};

/**
 * @return {number}
 */
MyStack.prototype.pop = function() {
    let size = this.queue.length;
    // 保留最后一个元素
    size--;
    while (size--) {
        this.queue.push(this.queue.shift());
    }
    return this.queue.shift();
};

/**
 * @return {number}
 */
MyStack.prototype.top = function() {
    const res = this.queue.pop();
    this.queue.push(res);
    return res;
};

/**
 * @return {boolean}
 */
MyStack.prototype.empty = function() {
    return !this.queue.length;

};

/**
 * Your MyStack object will be instantiated and called as such:
 * var obj = new MyStack()
 * obj.push(x)
 * var param_2 = obj.pop()
 * var param_3 = obj.top()
 * var param_4 = obj.empty()
 */

双队列实现

var MyStack = function() {
    this.queue1 = [];
    this.queue2 = [];

};

/** 
 * @param {number} x
 * @return {void}
 */
MyStack.prototype.push = function(x) {
    this.queue1.push(x);
};

/**
 * @return {number}
 */
MyStack.prototype.pop = function() {
    if (!this.queue1.length) {
        [this.queue1, this.queue2] = [this.queue2, this.queue1];
    }
    while (this.queue1.length > 1) {
        this.queue2.push(this.queue1.shift());
    }
    return this.queue1.shift();
};

/**
 * @return {number}
 */
MyStack.prototype.top = function() {
    const res = this.pop();
    this.push(res);
    return res;
};

/**
 * @return {boolean}
 */
MyStack.prototype.empty = function() {
    return !this.queue1.length && !this.queue2.length;
};

/**
 * Your MyStack object will be instantiated and called as such:
 * var obj = new MyStack()
 * obj.push(x)
 * var param_2 = obj.pop()
 * var param_3 = obj.top()
 * var param_4 = obj.empty()
 */