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 part1() {
  let data = getInput();
  const HEIGHT = data.length;
  const WIDTH = data[0].length;
  let currentDir = DIRECTIONS.UP;

  let actualPos = { x: 0, y: 0 };

  // Search initial pos
  for (let y = 0; y < HEIGHT; y++) {
    const x = data[y].indexOf("^");
    if (x == -1) continue;
    data[y][x] = "X";
    actualPos.y = y;
    actualPos.x = x;
  }
  // console.log(actualPos);

  // 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"));
}

part1();