手撕代码系列 (四)

class Scheduler {    constructor(max) {        this.queue = [];        this.max = max;        this.count = 0;    }
    add(time, order) {        const promise = () => {            return new Promise((resolve, reject) => {                setTimeout(() => {                    console.log(order);                    resolve();                }, time);            });        };        this.queue.push(promise);    }
    start() {        for (let i = 0; i < this.max; i++) {            this.request();        }    }
    request() {        if (!this.queue.length || this.count >= this.max) return;        this.count++;        this.queue            .shift()()            .then(() => {                this.count--;                this.request();            });    }}
// test:let scheduler = new Scheduler(2);scheduler.add(2000, '1');scheduler.add(200, '2');scheduler.add(500, '3');scheduler.add(800, '4');scheduler.add(1200, '5');scheduler.start(); // 2 3 4 1 5

/** * 统计前三的标签 * * @logic *  1.先拿到所有标签的标签名 *  2.对每个标签进行统计 *  3.倒序 *  4.截取前三项即可 */Object.entries(    [...document.querySelectorAll('*')]        .map(tag => tag.tagName)        .reduce((ret, i) => {            ret[i] = (ret[i] || 0) + 1;            return ret;        }, {}))    .sort((a, b) => b[1] - a[1])    .slice(0, 3)    .map(item => `${item[0]}: ${item[1]}`)    .join(',');
// test：// [//     ['SPAN', 451],//     ['A', 135],//     ['DIV', 106]// ]
// 统计页面中使用到的标签new Set([...document.querySelectorAll('*')].map(tag => tag.tagName));// Set(37) {'HTML', 'RELINGO-APP', 'DIV', 'HEAD', 'META', …}
// 统计每个标签使用的个数Object.entries(    [...document.querySelectorAll('*')]        .map(tag => tag.tagName)        .reduce((prev, next) => {            prev[next] = (prev[next] || 0) + 1;            return prev;        }, {}));
// test:// [//     ['HTML', 1]//     ['RELINGO-APP', 2]//     ['DIV', 106]//     ['HEAD', 1]//     ['META', 7]//     ['TITLE', 1]//     ['LINK', 71]//     ['SCRIPT', 8]// ]

function factorial(n) {    if (n <= 1) return 1;
    // return fibonacci(n - 1) + fibonacci(n - 2);    return n * factorial(n - 1);}
// test:console.log('factorial(5)', factorial(3)); // 6

class LRUCache {    constructor(capacity) {        this.cache = new Map();        this.max = capacity;    }
    get(key) {        if (this.cache.has(key)) {            let temp = this.cache.get(key);            // 删除当前项            this.cache.delete(key);            // 将当前项移到最前面            this.cache.set(key, temp);            return temp;        }        return -1;    }
    put(key, value) {        if (this.cache.has(key)) {            this.cache.delete(key);        } else {            // 如果缓存数 >= this.max 然后执行淘汰机制            // this.cache.keys().next().value：cache 中第一个值            if (this.cache.size >= this.max) {                this.cache.delete(this.cache.keys().next().value);            }        }        this.cache.set(key, value);    }}
// test:let lRUCache = new LRUCache(2);lRUCache.put(1, 1); // 缓存是 {1=1}lRUCache.put(2, 2); // 缓存是 {1=1, 2=2}lRUCache.get(1); // 返回 1lRUCache.put(3, 3); // 该操作会使得关键字 2 作废，缓存是 {3=3, 1=1}lRUCache.get(2); // 返回 -1 (未找到)lRUCache.put(4, 4); // 该操作会使得关键字 1 作废，缓存是 {4=4, 3=3}lRUCache.get(1); // 返回 -1 (未找到)lRUCache.get(3); // 返回 3lRUCache.get(4); // 返回 4console.log(lRUCache.cache.size);

/** * @param {Function} fn 方法 * @param {Number} time 间隔时间 */const MySetTimeout = (fn, time = 400) => {    let timer = setInterval(() => {        fn();        clearInterval(timer);    }, time);};
// test:MySetTimeout(() => {    console.log('12132');}, 3000);

/** * @param {Function} fn 方法 * @param {Number} timeout 间隔时间 */function MysetInterVal(fn, timeout = 1500) {    let timer = null;    const interval = () => {        fn();        timer = setTimeout(interval, timeout);    };
    setTimeout(interval, timeout);    return {        cancel: () => {            clearTimeout(timer);        },    };}
// test：let { cancel } = MysetInterVal(() => console.log(454545), 1500);setTimeout(() => {    cancel();}, 4000);