Number of Islands

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

    }
    int numIslands(vector<vector<char>>& grid) {
        int count=0;
        for(int i=0;i<grid.size();i++){
            for(int j =0;j<grid[0].size();j++){
                if(grid[i][j]=='1'){
                    f(grid,i,j);
                    count++;
                }
            }
        }
        return count;
    }
};