Advent of code 2023 - Day 3

day3.js

import {readFileLines} from '../utils/file.mjs';

const NUMBER_REGEX = /\d+/g;

const extractNumbers = (line, lineIndex) => {
  const numbers = [];
  let match;
  while ((match = NUMBER_REGEX.exec(line)) != null) {
    numbers.push({
      number: match[0],
      neighbours: getNeighbours(lineIndex, match.index, match[0]),
    });
  }
  return numbers;
}

const getNeighbours = (lineIndex, firstCharIndex, number) => [
  coord(lineIndex - 1, firstCharIndex - 1),
  coord(lineIndex, firstCharIndex - 1),
  coord(lineIndex + 1, firstCharIndex - 1),
  ...Array.from(number).flatMap((digit, index) => [
    coord(lineIndex - 1, firstCharIndex + index),
    coord(lineIndex + 1, firstCharIndex + index),
  ]),
  coord(lineIndex - 1, firstCharIndex + number.length),
  coord(lineIndex, firstCharIndex + number.length),
  coord(lineIndex + 1, firstCharIndex + number.length),
];

const coord = (line, char) => ({line, char});

const hashCoord = (coord) => JSON.stringify(coord);

const charExtractor = (lines) => (coord) => lines[coord.line]?.charAt(coord.char);

const isPart = (getChar) => (number) => number.neighbours.map(getChar).some(isSymbol);

const isSymbol = (char) => char && !Number(char) && char !== '.';

const addPartNumber = (sum, part) => sum + Number(part.number);

const indexGears = (getChar) => (gears, part) => {
  const gearCoords = part.neighbours.filter((coord) => isGear(getChar(coord)));

  if (!gearCoords.length) {
    return gears;
  }

  return {
    ...gears,
    ...Object.fromEntries(
      gearCoords.map(hashCoord)
                .map((hash) => [hash, gears[hash] ? new Set([...gears[hash], part]) : new Set([part])])
    ),
  };
};

const isGear = (char) => char === '*';

const hasTwoParts = (parts) => parts.size === 2;

const computeRatio = (parts) => Array.from(parts)
                                     .map((part) => Number(part.number))
                                     .reduce(Math.imul, 1);

const main = async () => {
  const lines = readFileLines(process.argv[2]);

  const getChar = charExtractor(lines);

  const parts = lines.flatMap(extractNumbers)
                     .filter(isPart(getChar));

  // Part 1 answer
  const partsSum = parts.reduce(addPartNumber, 0);

  const gears = parts.reduce(indexGears(getChar), {});

  // Part 2 answer
  const ratioSum = Object.values(gears)
                         .filter(hasTwoParts)
                         .map(computeRatio)
                         .reduce((x, y) => x + y, 0);

  console.log(partsSum);
  console.log(ratioSum);
};

main();