aoc-2024-day2-2.ts

const data = await Deno.readTextFile("./day2.txt");
const reports = data.split("\n").map((line) => line.split(/\s+/).map(Number));

function checkIsSafe(report: number[], index = 0, dampened = false): boolean {
  const a = report[index];
  const b = report[index + 1];
  const diff = b - a;
  const direction = report[1] - report[0] < 0 ? "dec" : "inc";
  const isLast = index + 1 === report.length;

  if (
    diff === 0 ||
    Math.abs(diff) > 3 ||
    (direction === "inc" && diff < 0) ||
    (direction === "dec" && diff > 0)
  ) {
    if (dampened) {
      return false;
    }

    if (isLast) {
      return true;
    }

    const dropBefore = checkIsSafe(
      report.toSpliced(Math.max(index - 1, 0), 1),
      Math.max(0, index - 2),
      true
    );

    if (dropBefore) {
      return true;
    }

    const dropCurrent =
      index === 0
        ? dropBefore
        : checkIsSafe(report.toSpliced(index, 1), Math.min(0, index - 1), true);

    if (dropCurrent) {
      return true;
    }

    const dropNext = checkIsSafe(report.toSpliced(index + 1, 1), index, true);

    if (dropNext) {
      return true;
    }

    return false;
  }

  if (isLast) {
    return true;
  }

  return checkIsSafe(report, index + 1, dampened);
}

let safe = 0;

for (const report of reports) {
  if (checkIsSafe(report)) {
    safe++;
  }
}

console.log("safe", safe);