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