numIslands.cpp

class Solution {
public:
    void dfs(int i , int j , int n , int m ,vector<vector<char>>& grid){
        if(i<0 || j<0 || i>=n || j>=m || grid[i][j] =='0' )return ;
        
        grid[i][j]='0';
        dfs(i+1,j,n,m,grid);
        dfs(i-1,j,n,m,grid);
        dfs(i,j-1,n,m,grid);
        dfs(i,j+1,n,m,grid);
    }
    int numIslands(vector<vector<char>>& grid) {
        int n = grid.size();
        if(n==0) return 0;
        int m = grid[0].size();
        int nIslands =0;
        for(int i =0 ; i<n;i++){
            for(int j =0 ; j<m;j++){
                if(grid[i][j]=='1'){
                    nIslands++;
                    dfs(i,j,n,m,grid);
                }
            }
        }
        return nIslands;
    }
};