question47.java

public class question47 { 
    public static int numIslands(char[][] grid) {
        if (grid == null || grid.length == 0) return 0;

        int count = 0;
        int rows = grid.length, cols = grid[0].length;

        for (int i = 0; i < rows; i++) {
            for (int j = 0; j < cols; j++) {
                if (grid[i][j] == '1') {
                    dfs(grid, i, j);
                    count++;
                }
            }
        }

        return count;
    }

    public static void dfs(char[][] grid, int i, int j) {
        int rows = grid.length, cols = grid[0].length;

        if (i < 0 || j < 0 || i >= rows || j >= cols || grid[i][j] == '0') return;

        grid[i][j] = '0';

        dfs(grid, i + 1, j); 
        dfs(grid, i - 1, j); 
        dfs(grid, i, j + 1); 
        dfs(grid, i, j - 1); 
    }
    public static void main(String[] args) {
        char[][] grid = {
            {'1','1','0','0','0'},
            {'1','1','0','0','0'},
            {'0','0','1','0','0'},
            {'0','0','0','1','1'}
        };

        System.out.println("Number of islands: " + numIslands(grid));
    }
}