graph division problem dfs

class Solution {
public:

    double dfs (unordered_map < string , vector < pair <string , double> > >  &graph, string cur, string dist, double &ans, unordered_map <string, bool> &vis)
    {
       if (cur == dist)
       {
           return true;
       }
       vis[cur] = true;

        vector <pair <string , double> > vec = graph[cur];

        for (int i = 0 ; i < vec.size(); i++ )
        {
            string eq = vec[i].first;
            double w = vec[i].second;

            if (vis[eq] == false)
            {
                vis[eq] = true;
                ans *= w;
               if ( dfs (graph, eq, dist, ans, vis))
               {
                   return true;
               }
                ans /= w;
                vis[eq] = false;
            }
        }
        return false;
    }
    vector<double> calcEquation(vector<vector<string>>& equations, vector<double>& values, vector<vector<string>>& queries) {

        unordered_map < string , vector < pair <string , double> > > graph;
        vector <double> res;
        int sz = equations.size();

        for (int i = 0 ; i < sz ; i++ )
        {

            string a = equations[i][0];
            string b = equations[i][1];

            double ans = values[i];

            graph[a].push_back ({b,ans});
            graph[b].push_back ({a,(1/ans)});
        }

        sz = queries.size();

        for (int i = 0 ; i <sz; i++ )
        {

            string a = queries[i][0];
            string b = queries[i][1];

            unordered_map <string, bool> vis;

            double ans = -1;
            if (graph.find(a) == graph.end() || graph.find(b) == graph.end())
            {
                res.push_back (ans);
                continue;
            }

            double dfs_ans = 1;
            bool path = dfs (graph, a, b,dfs_ans,vis);

            if (path)
            res.push_back (dfs_ans);
            else
                res.push_back (ans);

        }
        return res;
    }
};