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[JS Hacker Rank useful snippets] #JavaScript #competition
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const _ = require('lodash') | |
/////// REDUCE /////// | |
res = .reduce((acc, val) => { | |
return acc + val | |
}, 0) | |
err = decorators.reduce((err, decorator) => { | |
return decorator(err) | |
}, err) | |
_.uniq() | |
_.union() | |
_.intersection() | |
_.difference() | |
_.groupBy([6.1, 4.2, 6.3], Math.floor) | |
_.partition() | |
_.memoize(func, [resolver]) | |
// parse input | |
const [ l1, l2 ] = input.split('\n') | |
const numbers = l2.split(' ') | |
// fast arrays | |
let s = input.trim() | |
const u8in = Uint8Array.from(s, (c, i) => s.charCodeAt(i)) | |
const u8temp = u8in.slice(0) | |
console.log(String.fromCharCode(...u8out)) | |
///////////////////////////////////// | |
// number to formatted string | |
var num = 12345.6789 | |
const { format } = new Intl.NumberFormat('en', { | |
style: 'decimal', | |
maximumFractionDigits: 2, | |
minimumFractionDigits: 0, | |
}) | |
format(num) // 12345.68 | |
format(12345) // 12345 | |
// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/toPrecision | |
// # of digits after decimal point | |
num.toFixed() // '12346' rounding, no fractional part | |
num.toFixed(1) // '12345.7' rounding | |
num.toFixed(6) // '12345.678900' added zeros | |
(1.23e+20).toFixed(2) // '123000000000000000000.00' | |
// # of significant digits overall | |
num.toPrecision() // '12345.6789' no change | |
num.toPrecision(5) // '12346' rounded | |
num.toPrecision(2) // '1.2e+4' | |
num.toPrecision(1) // '1e+4' | |
number.toExponential // .e+. | |
///////////////////////////////////// | |
// left shift | |
const p1 = a.slice(0, k) | |
const p2 = a.slice(k) | |
p1.unshift(...p2) | |
console.log(p1.join(' ')) | |
// set | |
const seen = new Set() | |
seen.add(1) | |
mySet.has(1) | |
// Math | |
Math.abs(-5) // 5 | |
Math.sign( 3) // 1 | |
Math.sign(-3) // -1 | |
Math.sign( 0) // 0 | |
Math.max(1, 2, 3) | |
let max_ = Number.NEGATIVE_INFINITY | |
max_ = Math.max(max_ , ) | |
Math.min(1, 2, 3) | |
let min_ = Number.POSITIVE_INFINITY | |
min_ = Math.min(min_ , ) | |
Math.pow(2, 8) // 256 | |
Math.ceil( .95) // 1 | |
Math.ceil( 3) // 3 | |
Math.ceil(-0.95) // -0 | |
Math.ceil(-3) // -3 | |
Math.floor( 3.95) // 3 | |
Math.floor( 4 ) // 4 | |
Math.floor(-5.05) // -6 | |
Math.round( 20.49) // 20 | |
Math.round( 20.5) // 21 | |
Math.trunc(13.37) // 13 | |
Math.trunc(0.123) // 0 | |
Math.trunc(-0.123) // -0 | |
Math.fround(0) // 0 | |
Math.fround(1) // 1 | |
Math.fround(1.337) // 1.3370000123977661 | |
Math.fround(1.5) // 1.5 | |
// 32 bits | |
Math.imul(0xffffffff, 5) // -5 | |
Math.clz32(1) // 31 "count leading zeros" | |
Math.clz32(1000) // 22 | |
Math.clz32(true) // 31 | |
// fast arrays | |
var uint8 = new Uint8Array(2); | |
uint8[0] = 42; | |
Uint8ClampedArray | |
// misc | |
Number.EPSILON | |
Number.NEGATIVE_INFINITY | |
Number.POSITIVE_INFINITY |
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