Number of Islands

A grid is made of land (1) and water (0). An island is a group of land cells connected up, down, left or right (not diagonally). Count the islands.

Input:

• Line 1: rows cols.
• Then rows lines, each a string of cols characters (0 or 1).

Output: the number of islands.

1 <= rows, cols <= 50. There are no spaces inside a row.