Advent-of-Code-2022/6/solution.mjs

import { readFileSync } from 'node:fs';

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

function isValidMarker(marker) {
  return marker.split('').every((c, i, word) => word.lastIndexOf(c) === i);
}

function findMarker(markerLength) {
  for (let pos = markerLength; pos <= input.length; pos++) {
    const marker = input.slice(pos - markerLength, pos);
    if (isValidMarker(marker)) {
      return { marker, pos };
    }
  }
}

const packetMarker = findMarker(4);
if (packetMarker) {
  console.log(
    `Found packet marker: ${packetMarker.marker} after: ${packetMarker.pos} ` +
    `characters`
  );
}

const messageMarker = findMarker(14);
if (messageMarker) {
  console.log(
    `Found message marker: ${messageMarker.marker} after: ` +
    `${messageMarker.pos} characters`
  );
}