Number of Islands in a Grid

Given a 2D grid consisting of '1's (land) and '0's (water), write a function that counts 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 all surrounded by water. Input Format: - The first line contains two integers m (rows) and n (columns) of the grid. - The next m lines each contain a string of n characters ('0' or '1'). Output Format: - A single integer representing the number of islands. Example: Input: 4 5 11000 11000 00100 00011 Output: 3