adventofcode2025/04/code.js

import { readFileSync } from 'node:fs';

let sampleMode = false;
let usedArray = [];

const sampleArray = readFileSync('sample.txt').toString().split("\n");
const inputArray = readFileSync('input.txt').toString().split("\n");

if (sampleMode) {
  usedArray = [].concat(sampleArray);
} else {
  usedArray = [].concat(inputArray);
}

// Part One

console.time("part1");
let sum = 0;

for (let i = 0; i < usedArray.length; i++) {
  let row = usedArray[i];
  for (let j = 0; j < row.length; j++) {
    let cell = row[j];
    if (cell === '@') {
      let openSides = 0;
      const left = j > 0 ? row[j - 1] : '.';
      const right = j < row.length - 1 ? row[j + 1] : '.';
      const up = i > 0 ? usedArray[i - 1][j] : '.';
      const down = i < usedArray.length - 1 ? usedArray[i + 1][j] : '.';
      const upperLeft = i > 0 && j > 0 ? usedArray[i - 1][j - 1] : '.';
      const upperRight = i > 0 && j < row.length - 1 ? usedArray[i - 1][j + 1] : '.';
      const lowerLeft = i < usedArray.length - 1 && j > 0 ? usedArray[i + 1][j - 1] : '.';
      const lowerRight = i < usedArray.length - 1 && j < row.length - 1 ? usedArray[i + 1][j + 1] : '.';
      if (left === '.') {
        openSides++;
      }
      if (right === '.') {
        openSides++;
      }
      if (up === '.') {
        openSides++;
      }
      if (down === '.') {
        openSides++;
      }
      if (upperLeft === '.') {
        openSides++;
      }
      if (upperRight === '.') {
        openSides++;
      }
      if (lowerLeft === '.') {
        openSides++;
      }
      if (lowerRight === '.') {
        openSides++;
      }
      if (openSides >= 5) {
        sum++;
      }
    }
  }
}

console.timeEnd("part1");
console.log(sum);


// Part Two

let usedArray2 = [];
if (sampleMode) {
  usedArray2 = [].concat(sampleArray);
} else {
  usedArray2 = [].concat(inputArray);
}

console.time("part2");
let sum2 = 0;
let done = false;

while (!done) {
  getOpenSides(sum2, usedArray2);
}

console.timeEnd("part2");
console.log(sum2);

// functions

function getOpenSides(startingSum, usedArray) {
  const newSum = JSON.parse(JSON.stringify(startingSum));
  for (let i = 0; i < usedArray.length; i++) {
    let row = [...usedArray[i].split('')];
    for (let j = 0; j < row.length; j++) {
      let cell = row[j];
      if (cell === '@') {
        let openSides = 0;
        const left = j > 0 ? row[j - 1] : '.';
        const right = j < row.length - 1 ? row[j + 1] : '.';
        const up = i > 0 ? usedArray[i - 1][j] : '.';
        const down = i < usedArray.length - 1 ? usedArray[i + 1][j] : '.';
        const upperLeft = i > 0 && j > 0 ? usedArray[i - 1][j - 1] : '.';
        const upperRight = i > 0 && j < row.length - 1 ? usedArray[i - 1][j + 1] : '.';
        const lowerLeft = i < usedArray.length - 1 && j > 0 ? usedArray[i + 1][j - 1] : '.';
        const lowerRight = i < usedArray.length - 1 && j < row.length - 1 ? usedArray[i + 1][j + 1] : '.';
        if (left === '.') {
          openSides++;
        }
        if (right === '.') {
          openSides++;
        }
        if (up === '.') {
          openSides++;
        }
        if (down === '.') {
          openSides++;
        }
        if (upperLeft === '.') {
          openSides++;
        }
        if (upperRight === '.') {
          openSides++;
        }
        if (lowerLeft === '.') {
          openSides++;
        }
        if (lowerRight === '.') {
          openSides++;
        }
        if (openSides >= 5) {
          sum2++;
          row[j] = '.';
        }
      }
    }
    usedArray[i] = row.join('');
  }

  if (sum2 === newSum) {
    done = true;
  }
}