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class Graph {constructor(directed = true) {this.directed = directed;this.nodes = [];this.edges = new Map();}addNode(key, value = key) {this.nodes.push({ key, value });}addEdge(a, b, weight) {this.edges.set(JSON.stringify([a, b]), { a, b, weight });if (!this.directed)this.edges.set(JSON.stringify([b, a]), { a: b, b: a, weight });}removeNode(key) {this.nodes = this.nodes.filter(n => n.key !== key);[...this.edges.values()].forEach(({ a, b }) => {if (a === key || b === key) this.edges.delete(JSON.stringify([a, b]));});}removeEdge(a, b) {this.edges.delete(JSON.stringify([a, b]));if (!this.directed) this.edges.delete(JSON.stringify([b, a]));}findNode(key) {return this.nodes.find(x => x.key === key);}hasEdge(a, b) {return this.edges.has(JSON.stringify([a, b]));}setEdgeWeight(a, b, weight) {this.edges.set(JSON.stringify([a, b]), { a, b, weight });if (!this.directed)this.edges.set(JSON.stringify([b, a]), { a: b, b: a, weight });}getEdgeWeight(a, b) {return this.edges.get(JSON.stringify([a, b])).weight;}adjacent(key) {return [...this.edges.values()].reduce((acc, { a, b }) => {if (a === key) acc.push(b);return acc;}, []);}indegree(key) {return [...this.edges.values()].reduce((acc, { a, b }) => {if (b === key) acc++;return acc;}, 0);}outdegree(key) {return [...this.edges.values()].reduce((acc, { a, b }) => {if (a === key) acc++;return acc;}, 0);}}const g = new Graph();g.addNode('a');g.addNode('b');g.addNode('c');g.addNode('d');g.addEdge('a', 'c');g.addEdge('b', 'c');g.addEdge('c', 'b');g.addEdge('d', 'a');g.nodes.map(x => x.value); // ['a', 'b', 'c', 'd'][...g.edges.values()].map(({ a, b }) => `${a} => ${b}`);// ['a => c', 'b => c', 'c => b', 'd => a']g.adjacent('c'); // ['b']g.indegree('c'); // 2g.outdegree('c'); // 1g.hasEdge('d', 'a'); // trueg.hasEdge('a', 'd'); // falseg.removeEdge('c', 'b');[...g.edges.values()].map(({ a, b }) => `${a} => ${b}`);// ['a => c', 'b => c', 'd => a']g.removeNode('c');g.nodes.map(x => x.value); // ['a', 'b', 'd'][...g.edges.values()].map(({ a, b }) => `${a} => ${b}`);// ['d => a']g.setEdgeWeight('d', 'a', 5);g.getEdgeWeight('d', 'a'); // 5
const getSubsets = arr => arr.reduce((prev, curr) => prev.concat(prev.map(k => k.concat(curr))), [[]]);// ExamplesgetSubsets([1, 2]); // [[], [1], [2], [1, 2]]getSubsets([1, 2, 3]); // [[], [1], [2], [1, 2], [3], [1, 3], [2, 3], [1, 2, 3]]
const celsiusToFahrenheit = (celsius) => celsius * 9/5 + 32;const fahrenheitToCelsius = (fahrenheit) => (fahrenheit - 32) * 5/9;// ExamplescelsiusToFahrenheit(15); // 59celsiusToFahrenheit(0); // 32celsiusToFahrenheit(-20); // -4fahrenheitToCelsius(59); // 15fahrenheitToCelsius(32); // 0
require("dotenv").config();const mongoose = require("mongoose");const db = process.env.MONGO_URI;const connectDB = async () => {try {await mongoose.connect(db, {useNewUrlParser: true,useUnifiedTopology: true,useFindAndModify: false,useCreateIndex: true});console.log("MongoDB Connected");} catch (err) {console.error(err.message);}};module.exports = connectDB;
const formatDuration = ms => {if (ms < 0) ms = -ms;const time = {day: Math.floor(ms / 86400000),hour: Math.floor(ms / 3600000) % 24,minute: Math.floor(ms / 60000) % 60,second: Math.floor(ms / 1000) % 60,millisecond: Math.floor(ms) % 1000};return Object.entries(time).filter(val => val[1] !== 0).map(([key, val]) => `${val} ${key}${val !== 1 ? 's' : ''}`).join(', ');};formatDuration(1001); // '1 second, 1 millisecond'formatDuration(34325055574); // '397 days, 6 hours, 44 minutes, 15 seconds, 574 milliseconds'
const binomialCoefficient = (n, k) => {if (Number.isNaN(n) || Number.isNaN(k)) return NaN;if (k < 0 || k > n) return 0;if (k === 0 || k === n) return 1;if (k === 1 || k === n - 1) return n;if (n - k < k) k = n - k;let res = n;for (let j = 2; j <= k; j++) res *= (n - j + 1) / j;return Math.round(res);};binomialCoefficient(8, 2); // 28