Count the islands — ( Java, C# …)

Given a boolean matrix,find the number of islands.

What is an island?

A group of connected 1s forms an island. For example, the below matrix contains 5 islands

{1, 1, 0, 0, 0},
                    {0, 1, 0, 0, 1},
                    {1, 0, 0, 1, 1},
                    {0, 0, 0, 0, 0},
                    {1, 0, 1, 0, 1}

Input Format

Number of rows ,number of columns in the first line.

Followed by the matrix.

Output Format

Print the number of islands.

Sample Input

5 5 
1 1 0 0 0   
0 1 0 0 1
1 0 0 1 1
0 0 0 0 0
1 0 1 0 1

Sample Output

5

//C#
using System;
using System.Collections.Generic;
using System.IO;
class IslandMatrix {
    
    static int numIsland(int[][] grid)
    {
        if(grid == null || grid.Length == 0)
        {
            return 0;
        }

        int numIsland = 0;

        for(int i = 0; i < grid.Length; i++){
            for(int j = 0; j < grid[0].Length; j++){
                if(grid[i][j] == 1){
                    numIsland += dfs(grid, i, j);
                }
            }
        }
        return numIsland;
    }

    static int dfs(int[][] grid, int i, int j)
    {
        if(i < 0 || i >= grid.Length || j < 0 || j >= grid[i].Length || grid[i][j] == 0){
            return 0;
        }
        grid[i][j] = 0;
        dfs(grid, i + 1, j);
        dfs(grid, i - 1, j );
        dfs(grid, i, j + 1 );
        dfs(grid, i, j - 1 );

        dfs(grid, i + 1, j + 1 );
        dfs(grid, i + 1, j - 1 );
        dfs(grid, i - 1, j + 1 );
        dfs(grid, i - 1, j - 1 );

        return 1;
    }
    
    static void Main(String[] args) {
        /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution */
        int[] arrayMatrix = Array.ConvertAll(Console.ReadLine().Split(' '), arrTemp => Convert.ToInt32(arrTemp));
        
        int n = arrayMatrix[0];
        int m = arrayMatrix[1];
        int[][] arr = new int[n][];

        for (int i = 0; i < n; i++) {
            arr[i] = Array.ConvertAll(Console.ReadLine().Split(' '), arrTemp => Convert.ToInt32(arrTemp));
        }
        
        System.Console.WriteLine(numIsland(arr));
    }
}
//Java
import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class IslandMatrix {
    private static final Scanner scanner = new Scanner(System.in);

    public static int numIsland(int[][] grid) {
        if (grid == null || grid.length == 0) {
            return 0;
        }

        int numIsland = 0;

        for (int i = 0; i < grid.length; i++) {
            for (int j = 0; j < grid[0].length; j++) {
                if (grid[i][j] == 1) {
                    numIsland += dfs(grid, i, j);
                }
            }
        }
        return numIsland;
    }

    public static int dfs(int[][] grid, int i, int j) {
        if (i < 0 || i >= grid.length || j < 0 || j >= grid[i].length || grid[i][j] == 0) {
            return 0;
        }
        grid[i][j] = 0;
        dfs(grid, i + 1, j);
        dfs(grid, i - 1, j);
        dfs(grid, i, j + 1);
        dfs(grid, i, j - 1);

        dfs(grid, i + 1, j + 1);
        dfs(grid, i + 1, j - 1);
        dfs(grid, i - 1, j + 1);
        dfs(grid, i - 1, j - 1);

        return 1;
    }

    public static void main(String[] args) {

        String[] arrayLen = scanner.nextLine().split(" ");

        int n = Integer.parseInt(arrayLen[0]);
        int m = Integer.parseInt(arrayLen[1]);

        int[][] arr = new int[n][m];

        for (int i = 0; i < arr.length; i++) {
                String[] arrRowItems = scanner.nextLine().split(" ");
                scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");

                for (int j = 0; j < arr[i].length; j++) {
                        int arrItem = Integer.parseInt(arrRowItems[j]);
                        arr[i][j] = arrItem;
                }
        }

        System.out.println(numIsland(arr));
        scanner.close();
    }
}