Advent-of-Code-2022/3/solution.mjs

import { readFileSync } from 'node:fs';

const input = readFileSync('input', 'utf-8');

function priorityForItem(item) {
  const c = item.charCodeAt(0);
  return c - (c >= 97 ? 96 : 38)
}

const rucksacks = input
  .split('\n')
  .filter(line => {
    if (!line) return false;
    if (line.length % 2 !== 0) {
      throw new Error('Rucksack with unequal compartments');
    }
    return true;
  })
  .map(line => line.split(''))
  .map(rucksack => ([
    // compartment 1
    rucksack.slice(0, rucksack.length / 2),
    // compartment 2
    rucksack.slice(rucksack.length / 2)
  ]));

const sumOfPriorities = rucksacks
  .map(([compartment1, compartment2]) => {
    const commonItems = [...new Set(
      compartment1.filter(item => compartment2.includes(item))
    )];
    if (commonItems.length !== 1) {
      throw new Error('Unexpected number of common items');
    }
    return priorityForItem(commonItems[0]);
  })
  .reduce((total, priority) => total + priority, 0);

console.log(`Sum of priorities of common items: ${sumOfPriorities}`);

const elfRucksackGroups = rucksacks
  .reduce((groups, rucksack) => {
    let group = groups[groups.length - 1];
    if (group.length >= 3) {
      group = [];
      groups.push(group);
    }
    group.push(rucksack);
    return groups;
  }, [[]]);

const commonItemsInGroup = elfRucksackGroups
  .map(group => group
    .reduce((itemsA, itemsB) => {
      itemsA = [...new Set(itemsA.flat())];
      itemsB = [...new Set(itemsB.flat())];
      return itemsA.filter(item => itemsB.includes(item))
    })
  )

const badgePriorities = commonItemsInGroup
  .map(items => priorityForItem(items[0]))
  .reduce((total, priority) => total + priority, 0)

console.log(`Sum of badge priorities: ${badgePriorities}`);