AdventOfCode2024/09/index.ts

import fs from "node:fs";
import { printTime, now, toNum } from "../util";

const test = false;

const data = fs.readFileSync(
  test ? "./inputs/testinput" : "./inputs/input",
  "utf8"
);

let timer = now.instant();

let sparceArray = data
  .split("\n")
  .slice(0, -1)[0]
  .split("")
  .map(toNum)
  .reduce((disk, curr, index) => {
    const fill = index % 2 === 0 ? index / 2 : -1; // -1 represents free space
    return [...disk, ...Array.from({ length: curr }, () => fill)];
  }, [] as Array<number>);

let rightCursor = sparceArray.length - 1;
let leftCursor = 0;
while (leftCursor < rightCursor) {
  if (sparceArray[leftCursor] === -1) {
    while (sparceArray[rightCursor] === -1) {
      rightCursor--;
    }
    if (leftCursor > rightCursor) {
      // don't let them overrun each other
      break;
    }
    sparceArray[leftCursor] = sparceArray[rightCursor];
    sparceArray[rightCursor] = -1;
  }
  leftCursor++;
}

console.log(
  "part one:",
  sparceArray.reduce((checksum, curr, i) => {
    if (curr !== -1) {
      return checksum + curr * i;
    }
    return checksum;
  }, 0),
  printTime(now.instant().since(timer))
);

// timer = now.instant();
// console.log(
//   "part two:",
//   data.split("\n").slice(0, -1),
//   printTime(now.instant().since(timer))
// );