d10.ts

import { Day, RegisterDay } from "../Day.ts";

@RegisterDay(2015, 10)
export class Day10 extends Day {
  override partOne(): string {
    const input = this.readInput().split("");
    const result = runGame(input, 40);

    return result.length.toString();
  }

  override partTwo(): string {
    const input = this.readInput().split("");
    const result = runGame(input, 50);

    return result.length.toString();
  }
}

function runGame(chars: string[], times: number): string[] {
  let latestChars = chars;
  for (let n = 0; n < times; n++) {
    const newChars = [];
    for (let i = 0; i < latestChars.length;) {
      const value = latestChars[i];

      if (i == latestChars.length - 1) {
        newChars.push("1");
        newChars.push(value);
        i++;
        continue;
      }

      let j = 1;
      while (latestChars[i + j] == value) {
        j += 1;
      }

      newChars.push(j.toString());
      newChars.push(value);
      i += j;
    }

    latestChars = newChars;
  }

  return latestChars;
}