```
class Solution {
private:
int row, column;
void traverse(vector<vector<char>>& grid, int r, int c)
{
grid[r][c] = '0';
if(r-1>-1 && grid[r-1][c]=='1') traverse(grid, r-1, c);
if(c-1>-1 && grid[r][c-1]=='1') traverse(grid, r, c-1);
if(r+1<row && grid[r+1][c]=='1') traverse(grid, r+1, c);
if(c+1<column && grid[r][c+1]=='1') traverse(grid, r, c+1);
}
public:
int numIslands(vector<vector<char>>& grid) {
row=grid.size();
if(!row) return 0;
column=grid[0].size();
int count = 0;
for(int r = 0; r < row; r++)
for(int c = 0; c < column; c++)
if(grid[r][c] == '1') count++,traverse(grid, r, c);
return count;
}
};
```