[JS Hacker Rank useful snippets] #JavaScript #competition

hackerrank.js

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

// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/toPrecision
var num = 12345.6789
// # 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'

var num = 12345.6789
// # 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