959

class Solution {
int g[100][100];
int r, c;

public:
    int regionsBySlashes(vector<string>& grid) {
        // Expand the given grid.
        for(int i=0; i<grid.size(); i++)
            for(int j=0; j<grid[i].length(); j++){
                int x = i*3, y = j*3;
                if(grid[i][j] == '/')
                    g[x][y+2] = g[x+1][y+1] = g[x+2][y] = 1;
                else if(grid[i][j] == '\\')
                    g[x][y] = g[x+1][y+1] = g[x+2][y+2] = 1;
            }

        r = 3*grid.size();
        c = 3*grid.size();
        // Find number of connected components.
        int components = 0;
        for(int i=0; i<r; i++)
            for(int j=0; j<c; j++)
                if(!g[i][j]){
                    components++;
                    dfs(i, j);
                }
        return components;
    }

    void dfs(int row, int col){
        if(row<0 || row>=r || col<0 || col>=c || g[row][col] == 1) return;
        g[row][col] = 1;
        dfs(row+1, col);
        dfs(row-1, col);
        dfs(row, col+1);
        dfs(row, col-1);
    }

};