advent-of-code-2024/day-6/main.js

import fs from "node:fs";

const DIRECTIONS = {
  UP: "up",
  DOWN: "down",
  LEFT: "left",
  RIGHT: "right",
};

function rotate(currentDir) {
  switch (currentDir) {
    case DIRECTIONS.UP:
      return DIRECTIONS.RIGHT;
    case DIRECTIONS.RIGHT:
      return DIRECTIONS.DOWN;
    case DIRECTIONS.DOWN:
      return DIRECTIONS.LEFT;
    case DIRECTIONS.LEFT:
      return DIRECTIONS.UP;
  }
}

function getInput() {
  const data = fs
    .readFileSync("input2.txt", "utf8")
    .split("\n")
    .map((line) => line.split(""));
  return data;
}

function getStart(data) {
  const HEIGHT = data.length;
  let actualPos = { x: 0, y: 0 };

  for (let y = 0; y < HEIGHT; y++) {
    const x = data[y].indexOf("^");
    if (x == -1) continue;
    actualPos.y = y;
    actualPos.x = x;
  }
  return actualPos;
}

function detectLoop(obstacle) {
  let data = getInput();
  data[obstacle[0]][obstacle[1]] = "#";
  let currentDir = DIRECTIONS.UP;
  let actualPos = getStart(data);
  data[actualPos.y][actualPos.x] = ".";
  let counter = 1;
  let nextStep = null;
  let newX = null;
  let newY = null;
  while (true) {
    switch (currentDir) {
      case DIRECTIONS.UP:
        newY = actualPos.y - 1;
        newX = actualPos.x;
        break;
      case DIRECTIONS.DOWN:
        newY = actualPos.y + 1;
        newX = actualPos.x;
        break;
      case DIRECTIONS.LEFT:
        newY = actualPos.y;
        newX = actualPos.x - 1;
        break;
      case DIRECTIONS.RIGHT:
        newY = actualPos.y;
        newX = actualPos.x + 1;
        break;
    }
    nextStep = (data[newY] ?? [])[newX];
    if (nextStep == undefined) return false;
    if (nextStep == ".") {
      // data[newY][newX] = "X";
      actualPos.y = newY;
      actualPos.x = newX;
      counter++;
      if (counter >= 20000) return true;
    } else {
      currentDir = rotate(currentDir);
    }
  }
}

function part1(data = getInput()) {
  let currentDir = DIRECTIONS.UP;
  let actualPos = getStart(data);
  data[actualPos.y][actualPos.x] = "X";

  // Start algorithm
  let counter = 1;
  let nextStep = null;
  let newX = null;
  let newY = null;
  while (true) {
    switch (currentDir) {
      case DIRECTIONS.UP:
        newY = actualPos.y - 1;
        newX = actualPos.x;
        break;
      case DIRECTIONS.DOWN:
        newY = actualPos.y + 1;
        newX = actualPos.x;
        break;
      case DIRECTIONS.LEFT:
        newY = actualPos.y;
        newX = actualPos.x - 1;
        break;
      case DIRECTIONS.RIGHT:
        newY = actualPos.y;
        newX = actualPos.x + 1;
        break;
    }
    nextStep = (data[newY] ?? [])[newX];
    if (nextStep == undefined) break;
    if (nextStep == ".") {
      data[newY][newX] = "X";
      actualPos.y = newY;
      actualPos.x = newX;
      counter++;
    } else if (nextStep == "X") {
      actualPos.y = newY;
      actualPos.x = newX;
    } else {
      currentDir = rotate(currentDir);
    }
  }
  console.log(counter);
  // print board
  // console.log(data.map((line) => line.join("")).join("\n"));
}

function part2() {
  let data = getInput();

  let actualPos = getStart(data);

  let possibleObstacle = [];
  for (let y in data) {
    for (let x in data) {
      if (data[y][x] == "." || (y != actualPos.y && x != actualPos.x)) {
        possibleObstacle.push([y, x]);
      }
    }
  }

  let counter = 0;
  for (const obstacle of possibleObstacle) {
    let innerData = getInput();
    if (detectLoop(obstacle)) {
      counter++;
    }
  }
  console.log(counter);
}

console.log("Part 1:");
part1();

console.log("Part 2:");
part2();