Advent-of-Code-2022/13/solution.mjs

import { readFileSync } from 'node:fs';

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

const pairs = input
  .split('\n\n')
  .map(pair => pair
    .split('\n')
    .filter(line => line)
    .map(line => JSON.parse(line))
  );

export function compare(left, right) {
  const leftIsArray = Array.isArray(left);
  const rightIsArray = Array.isArray(right);
  const compareArrays = leftIsArray || rightIsArray;
  if (leftIsArray && !rightIsArray) {
    right = [right];
  }
  if (rightIsArray && !leftIsArray) {
    left = [left];
  }

  if (compareArrays) {
    for (let i = 0; i < Math.max(left.length, right.length); i++) {
      if (i >= left.length) return -1;
      if (i >= right.length) return 1;
      
      const result = compare(left[i], right[i]);
      if (result !== 0) return result;
    }
    return 0;
  } else {
    return (left - right) / Math.abs(left - right || 1);
  }
}

const sumOfIndices = pairs
  .map(([left, right], i) => [i + 1, compare(left, right)])
  .filter(([_index, result]) => result === -1)
  .reduce((total, [index, _result]) => total + index, 0);

console.log(`Sum of correctly ordered inices: ${sumOfIndices}`);

const dividerPackets = [[[2]], [[6]]];
const allPackets = [...pairs.flat(), ...dividerPackets];
allPackets.sort(compare);

const decoderKey = dividerPackets
  .map(packet => allPackets.indexOf(packet) + 1)
  .reduce((total, index) => total * index);

console.log(`Decoder key: ${decoderKey}`);