aoc 2019 day 4 solution

d4.js

const parse = text => text.split("-").map(bound => +bound);
const range = (upperBound, lowerBound = 0) =>
  [...Array(upperBound - lowerBound).keys()]
    .map(i => i + lowerBound)
    .map(i => `${i}`);

const generate = bounds => range(bounds[1], bounds[0]);
const rule1 = /^0*1*2*3*4*5*6*7*8*9*$/; //number to the right is greater than or equal to previous number
const rule2 = /\d*(\d)\1\d*$/; //there is at least one duplicate neighbor
const rule3 = sequence =>
  sequence
    .split(/(?<=(.))(?!\1|$)/) //split into groups of duplicate numbers as well as single numbers
    .reduce((exactlyTwo, el) => (el.length === 2 ? true : exactlyTwo), false);
const p1 = generate(parse(input))
  .filter(rule1.test.bind(rule1))
  .filter(rule2.test.bind(rule2));

const p2 = p1.filter(rule3);
console.log(p1.length);
console.log(p2.length);