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