Count Unguarded Cells in the Grid

export function countUnguarded(
  m: number,
  n: number,
  guards: number[][],
  walls: number[][],
): number {
  const grid = Array.from({ length: m }, () => new Array(n).fill(0));
  const directions = [
    [0, 1],
    [0, -1],
    [1, 0],
    [-1, 0],
  ];
  guards.forEach(([y, x]) => {
    grid[y][x] = 2;
  });
  walls.forEach(([y, x]) => {
    grid[y][x] = 3;
  });
 
  for (const [y, x] of guards) {
    for (const [dy, dx] of directions) {
      dfs(grid, y + dy, x + dx, dy, dx);
    }
  }
 
  return grid.reduce((prev, row) => prev + row.filter((v) => v === 0).length, 0);
}
 
function dfs(grid: number[][], y: number, x: number, dy: number, dx: number): void {
  if (!isUnguarded(grid, y, x)) {
    return;
  }
  grid[y][x] = 1;
  dfs(grid, y + dy, x + dx, dy, dx);
}
 
function isUnguarded(grid: number[][], y: number, x: number): boolean {
  const [m, n] = [grid.length, grid[0].length];
  return 0 <= y && y < m && 0 <= x && x < n && grid[y][x] !== 2 && grid[y][x] !== 3;
}