Given an m x n 2D grid map of '1’s which represents land and '0’s that represents water, return the number of islands. Assume that the boundary cases - which is all four edges of the grid are surrounded by water

Web Development
,
#1

Constraints are:

m == grid.length
n == grid[i].length
1 <= m, n <= 300
grid[i][j] can only be ‘0’ or ‘1’.

Example:
Input: grid = [
[“1” , “1” , “1” , “0” , “0”],
[“1” , “1” , “0” , “0” , “0”],
[“0” , “0” , “1” , “0” , “1”],
[“0” , “0” , “0” , “1” , “1”]
]
Output: 3

Solution:

class InterviewBit {
public int numberOfIslands(char[][] grid) {
if(grid==null || grid.length==0||grid[0].length==0)
return 0;

        int m = grid.length;
        int n = grid[0].length;

        int count=0;
        for(int i=0; i<m; i++){
            for(int j=0; j<n; j++){
                if(grid[i][j]=='1'){
                    count++;
                    mergeIslands(grid, i, j);
                }
            }
        }

        return count;
    }

    public void mergeIslands(char[][] grid, int i, int j){
        int m=grid.length;
        int n=grid[0].length;

        if(i<0||i>=m||j<0||j>=n||grid[i][j]!='1')
            return;

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

        mergeIslands(grid, i-1, j);
        mergeIslands(grid, i+1, j);
        mergeIslands(grid, i, j-1);
        mergeIslands(grid, i, j+1);
    }