Find the Number of Islands (not mutating argument)

from typing import List

from collections import deque
def count_number_of_islands(grid: List[List[int]]) -> int:
    M, N = len(grid), len(grid[0])
    def get_neighbors(r, c):
        offsets = [(-1, 0), (0, -1), (0, +1), (+1, 0)]  # NWES
        return [(r+o[0], c+o[1]) for o in offsets
                if (0 <= r+o[0] and r+o[0] < M) and (0 <= c+o[1] and c+o[1] < N)
                and grid[r+o[0]][c+o[1]]]
    def bfs(r, c, visited, islands):  # visit adjacent 1s starting at (r,c)
        queue, island = deque([(r, c)]), []
        while len(queue):
            c_r, c_c = queue.popleft()  # cell coord
            island.append((c_r, c_c))
            neighbors = get_neighbors(c_r, c_c)
            [queue.append(n) for n in neighbors if n not in visited]
            [visited.add(n) for n in neighbors]
        islands.append(island)
    visited, islands = set(), [] # matrix also works for visited
    for r in range(M):
        for c in range(N):
            if (r, c) in visited:  # skip previously discovered island
                continue
            elif grid[r][c] == 1:  # new island, mark adjacent 1s visited
                bfs(r, c, visited, islands)
            else:  # 0, mark visited
                visited.add((r, c))
    return len(islands)

if __name__ == '__main__':
    grid = [[int(x) for x in input().split()] for _ in range(int(input()))]
    res = count_number_of_islands(grid)
    print(res)