advent-of-code/2020/07/part2.js

const fs = require('fs');
const OWN_BAG = 'shiny gold';

function parseLine(line) {
  let [ self, others ] = line.trim().split(" bags contain ");
  if (self === undefined || others === undefined) return [];
  if (others == "no other bags.") return []; // [{a: self, b: null, count: 0}];
  others = others.replace(".", "").replace(/bags?/g, "").split(",");

  return  others.map((other) => {
    let [ num, ...rest ] = other.trim().split(' ');
    return { a: self, b: rest.join(' '), count: Number(num) };
  });
}

fs.readFile('input', (err, data) => {
  if (err) throw err;
  let rules = data.toString().split("\n").map( parseLine ).flat();

  let bags = {};
  rules.forEach((rule) => {
    let parent = bags[rule.a] || {spec: rule.a};
    let child = bags[rule.b] || {spec: rule.b};

    if (!child.hasOwnProperty('parent')) child.parent = parent;
    if (!parent.hasOwnProperty('children')) parent.children = [];
    parent.children.push({ count: rule.count, bag: child });

    bags[rule.a] = parent;
    bags[rule.b] = child;
  });

  let bagCount = function(bag, self_count) {
    if (!bag.children) return self_count;
    return self_count + (bag.children.map((node) => bagCount(node.bag, node.count)).reduce((a,b) => a+b) * self_count);
  };

  let result = bags[OWN_BAG].children.map((node) => bagCount(node.bag, node.count)).reduce((a,b) => (a+b));

  console.log(result);
});