day11.js

const fs = require('fs').promises;

const partOne = (grid) => {
  let numChanges = 1;
  while (numChanges > 0) {
    numChanges = 0;
    const copyOfGrid = [];
    for (let row = 0; row < grid.length; row++) {
      const gridRow = grid[row];
      copyOfGrid.push([...gridRow]);
    }

    for (let row = 0; row < grid.length; row++) {
      for (let col = 0; col < grid[row].length; col++) {
        const seat = grid[row][col];
        if (seat === '.') {
          continue;
        }

        let countEmpty = 0;
        for (let nextRow = -1; nextRow < 2; nextRow++) {
          for (let nextCol = -1; nextCol < 2; nextCol++) {
            if (nextRow === 0 && nextCol === 0) continue;

            if (row + nextRow < 0 || row + nextRow >= grid.length) {
              countEmpty++;
              continue;
            }

            if (col + nextCol < 0 || col + nextCol >= grid[0].length) {
              countEmpty++;
              continue;
            }

            if (grid[row + nextRow][col + nextCol] !== '#') {
              countEmpty++;
            }
          }
        }

        if (countEmpty === 8 && seat === 'L') {
          copyOfGrid[row][col] = '#';
          numChanges++;
        } else if (seat === '#' && countEmpty <= 4) {
          copyOfGrid[row][col] = 'L';
          numChanges++;
        }
      }
    }

    grid = copyOfGrid;
  }

  let countPeople = 0;
  for (let row = 0; row < grid.length; row++) {
    for (let col = 0; col < grid.length; col++) {
      if (grid[row][col] === '#') countPeople++;
    }
  }
  return countPeople;
};

const partTwo = (grid) => {
  let numChanges = 1;
  while (numChanges > 0) {
    numChanges = 0;
    const copyOfGrid = [];
    for (let row = 0; row < grid.length; row++) {
      const gridRow = grid[row];
      copyOfGrid.push([...gridRow]);
    }

    for (let row = 0; row < grid.length; row++) {
      for (let col = 0; col < grid[row].length; col++) {
        const seat = grid[row][col];
        if (seat === '.') {
          continue;
        }

        let countEmpty = 0;

        const movements = [
          [-1, -1],
          [-1, 0],
          [-1, 1],
          [0, -1],
          [0, 1],
          [1, -1],
          [1, 0],
          [1, 1],
        ];
        movements.forEach(([deltaX, deltaY]) => {
          let nextRow = row;
          let nextCol = col;
          while (true) {
            nextRow += deltaX;
            nextCol += deltaY;

            if (nextRow < 0 || nextRow >= grid.length) {
              countEmpty++;
              break;
            }

            if (nextCol < 0 || nextCol >= grid[0].length) {
              countEmpty++;
              break;
            }

            if (grid[nextRow][nextCol] === 'L') {
              countEmpty++;
              break;
            }

            if (grid[nextRow][nextCol] === '#') {
              break;
            }
          }
        });

        if (countEmpty === 8 && seat === 'L') {
          copyOfGrid[row][col] = '#';
          numChanges++;
        } else if (seat === '#' && countEmpty <= 3) {
          copyOfGrid[row][col] = 'L';
          numChanges++;
        }
      }
    }

    grid = copyOfGrid;
  }

  let countPeople = 0;
  for (let row = 0; row < grid.length; row++) {
    for (let col = 0; col < grid.length; col++) {
      if (grid[row][col] === '#') countPeople++;
    }
  }
  return countPeople;
};

(async () => {
  console.log(`Reading input from ${__dirname}/${process.argv[2]}.txt`);
  const inputData = await fs.readFile(`${__dirname}/${process.argv[2]}.txt`);
  const inputs = inputData
    .toString()
    .split('\n')
    .filter((n) => n);

  let grid = [];
  inputs.forEach((line) => {
    const row = [];
    line.split('').forEach((s) => {
      row.push(s);
    });
    grid.push(row);
  });

  console.log('partOne', partOne(grid));

  console.log('partTwo', partTwo(grid));
})();