Advent of Code - Day 3

part2.js

const { readFile } = require("fs/promises");

function isUppercase(letter) {
  return letter.toLowerCase() !== letter;
}

const alphaVal = (s) => s.toLowerCase().charCodeAt(0) - 97 + 1;

function letterToPriority(letter) {
  return alphaVal(letter) + (isUppercase(letter) ? 26 : 0);
}

function findCommonLetter(threeLines) {
  for (const letter of threeLines[0]) {
    const inSecondLine = threeLines[1].includes(letter);
    const inThirdLine = threeLines[2].includes(letter);
    if (inSecondLine && inThirdLine) {
      return letter;
    }
  }
}

function parseRawInput(rawInput) {
  const lines = rawInput.split("\n");
  let i = 0;
  const groupOfThrees = [];
  let currentGroup;
  for (const line of lines) {
    if (i % 3 === 0) {
      currentGroup = [];
      groupOfThrees.push(currentGroup);
    }
    currentGroup.push(line);
    i++;
  }

  return groupOfThrees.map((group) =>
    letterToPriority(findCommonLetter(group))
  );
}

async function step2() {
  const path = "./input.txt";
  const content = await readFile(path, { encoding: "utf-8" });
  const rucksack = parseRawInput(content);
  const sum = rucksack.reduce((a, b) => a + b, 0);

  console.log(sum);
}

step2();