num Islands, Java - rextester

num Islands

//'main' method must be in a class 'Rextester'.
//Compiler version 1.8.0_111

import java.util.*;
import java.lang.*;

class Rextester
{  
    public static void main(String args[])
    {
        System.out.println("Hello, World!");

char[][] grid = new char[4][5];
        for(int i = 0;i<grid.length;i++){
            for(int j = 0;j<grid[i].length;j++){
                grid[i][j]='0';
            }
        }

grid[0][0] = '1';
        grid[0][1] = '1';
        grid[0][2] = '1';
        grid[0][3] = '1';
        grid[1][0] = '1';
        grid[1][1] = '1';
        grid[1][3] = '1';
        grid[2][0] = '1';
        grid[2][1] = '1';

System.out.println(numIslands(grid));
    }

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

//go through each element
        //if it's 1, increment count. 
        //Make it 0
        //do bfs on it until 0 comes on all sides.
        
        int count = 0;

for(int i=0;i<grid.length;i++){
            for(int j = 0;j<grid[i].length;j++){
                if(grid[i][j]=='1'){
                    count +=1;
                    //Go DFS
                    DFS(grid,i,j);
                }
            }
        }
    
        return count;
    }

public static void DFS(char[][] grid, int row,int col){
        int nr = grid.length;
        int nc = grid[0].length;
        if(row>nr || row<0 || col>nc || col<0 || grid[row][col]=='0')
            return;

grid[row][col]='0';

DFS(grid,row-1,col);
        DFS(grid,row+1,col);
        DFS(grid,row,col-1);
        DFS(grid,row,col+1);
    }

}


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