Advent of Code (Day 13 Part 2)

aoc-13-2.js

const fs = require('fs');
const INPUT = fs.readFileSync('./input.txt', 'utf-8').split('\n');
const PERSON_ATTRIBUTES_REGEX = /(\w+) would (\w+) (\d+) happiness units by sitting next to (\w+)./;

// Generate all possible permutations for an array
const permute = input => {
  const array = Array.from(input);
  const permute = (res, item, key, arr) => {
    return res.concat(arr.length > 1 && arr.slice(0, key).concat(arr.slice(key + 1)).reduce(permute, []).map(perm => [item].concat(perm)) || item);
  };

  return array.reduce(permute, []);
};

// Parse input and return map with attributes of each person
const getPersonAttributes = input => {
  return input.reduce((map, person) => {
    const parsed = person.match(PERSON_ATTRIBUTES_REGEX);
    const name = parsed[1];
    const isLose = parsed[2] === 'lose';
    const count = +parsed[3];
    const neighbour = parsed[4];

    map.set(`${name} -> ${neighbour}`, isLose ? -count : count);
    map.set(`ghaiklor -> ${name}`, 0);
    map.set(`${name} -> ghaiklor`, 0);

    return map;
  }, new Map());
};

// Get attendees list
const getAttendees = input => {
  return input.reduce((set, person) => {
    const parsed = person.match(PERSON_ATTRIBUTES_REGEX);
    return set.add(parsed[1]);
  }, new Set()).add('ghaiklor');
};

// Get all persons' attributes
const personAttributes = getPersonAttributes(INPUT);

// Get all possible permutations of the guests
const allPossiblePermutations = permute(getAttendees(INPUT));

const totalHappinnes = allPossiblePermutations.reduce((totalHappiness, permutation) => {
  const total = permutation.reduce((total, person, index, arr) => {
    const leftOne = arr[index - 1 < 0 ? arr.length - 1 : index - 1];
    const rightOne = arr[index + 1 > arr.length - 1 ? 0 : index + 1];

    total += personAttributes.get(`${person} -> ${leftOne}`);
    total += personAttributes.get(`${person} -> ${rightOne}`);

    return total;
  }, 0);

  return total > totalHappiness ? total : totalHappiness;
}, 0);

console.log(totalHappinnes);