Walls and Gates

def wallsAndGates(self, rooms: List[List[int]]) -> None: """ Do not return anything, modify rooms in-place instead. """ nrows, ncols = len(rooms), len(rooms[0]) q = deque() INF = 2147483647 for r in range(nrows): for c in range(ncols): if rooms[r][c] == 0: q.append((r, c)) level = 1 while q: for _ in range(len(q)): r, c = q.popleft() for dr, dc in [(0, 1), (0, -1), (1, 0), (-1, 0)]: nr, nc = r + dr, c + dc if nr >= 0 and nr < nrows and nc >= 0 and nc < ncols and rooms[nr][nc] == INF: q.append((nr, nc)) rooms[nr][nc] = level level += 1