Count Number of Islands in 2D Grid Map

bloomberg Given a 2D grid map of '1's (land) and '0's (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are surrounded by water. Implement a function to count the number of islands. Example Input 4 5 11000 11000 00100 00011