In 2D binary matrix find the number of islands

Question

I am trying to count the number of islands (a group of connected 1s forms an island) in a 2D binary matrix.

Example:

[
[1, 1, 0, 0, 0],
[0, 1, 0, 0,          


        

Answer 1

Your algorithm is almost correct except for the line 21:

if r != i and c != j:
    cnt += count_houses(mat, visited, r, c)

Instead you want to use or as you want to continue counting provided at least one of the coordinate is not the same as your center.

if r != i or c != j:
    cnt += count_houses(mat, visited, r, c)

An alternate and more intuitive way to write this would be the following

if (r, c) != (i, j):
    cnt += count_houses(mat, visited, r, c)