Day 4Printing Department

View puzzle description on Advent of Code

I was expecting part 2 to be more complicated than it turned out to be, so this all ended up being pretty straightforward.

I could tidy up my solution slightly by not having removeRolls mutate the original grid, but it's no big deal that it does.

type Grid = string[][];


const RADIUS = 1;
const ROLL = '@';


const createGridChecker =
  (grid: Grid) =>
  (centerY: number, centerX: number): boolean => {
    const maxX = grid[0].length - 1;
    const maxY = grid.length - 1;


    let adjacentRolls = 0;


    for (let dy = -1 * RADIUS; dy <= RADIUS; dy++) {
      for (let dx = -1 * RADIUS; dx <= RADIUS; dx++) {
        // We don't care about the center cell
        if (dx === 0 && dy === 0) continue;


        const x = centerX + dx;
        const y = centerY + dy;


        if (x < 0 || x > maxX || y < 0 || y > maxY) continue;


        if (grid[y][x] === ROLL) {
          adjacentRolls += 1;
        }


        if (adjacentRolls >= 4) {
          return false;
        }
      }
    }


    return true;
  };


export default (input: string): number => {
  const grid = input.split('\n').map(line => line.split('')) as Grid;


  const rollIsAccessible = createGridChecker(grid);


  let accessibleRolls = 0;


  for (let y = 0; y < grid.length; y++) {
    for (let x = 0; x < grid[0].length; x++) {
      if (grid[y][x] === ROLL && rollIsAccessible(y, x)) {
        accessibleRolls += 1;
      }
    }
  }


  return accessibleRolls;
};