Finding shortest paths of a C ++ directed graph

For the last week I have implemented Digraph by parsing the input file. The graph has no cycles. I successfully created a graph, used methods to return the number of vertices and edges, and rendered a topological view of the graph. The schedule consists of different core courses and their prerequisites. Here is my graph:

class vertex{
public:
    typedef std::pair<int, vertex*> ve;     
    std::vector<ve> adjacency;              
    std::string course;                     
    vertex(std::string c){
        course = c;
    }
};

class Digraph{
public:
    typedef std::map<std::string, vertex *> vmap;           
    vmap work;
    typedef std::unordered_set<vertex*> marksSet;           
    marksSet marks;
    typedef std::deque<vertex*> stack;                      
    stack topo;
    void dfs(vertex* vcur);                                 
    void addVertex(std::string&);                           
    void addEdge(std::string& from, std::string& to, int cost);     
    int getNumVertices();                                   
    int getNumEdges();                                      
    void getTopoSort();                                     

};

      

        
        
        
      

    

Implementation

//function to add vertex to the graph
void Digraph::addVertex(std::string& course){
    vmap::iterator iter = work.begin();
    iter = work.find(course);
    if(iter == work.end()){
        vertex *v;
        v = new vertex(course);
        work[course] = v;
        return;
    }
}

//method to add edges to the graph
void Digraph::addEdge(std::string& from, std::string& to, int cost){
    vertex *f = (work.find(from)->second);
    vertex *t = (work.find(to)->second);
    std::pair<int, vertex *> edge = std::make_pair(cost, t);
    f->adjacency.push_back(edge);
}

//method to return the number of vertices in the graph
int Digraph::getNumVertices(){
    return work.size();
}

//method to return the number of edges in the graph
int Digraph::getNumEdges(){
    int count = 0;
    for (const auto & v : work) {
         count += v.second->adjacency.size();
     }
     return count;
}

//recursive function used by the topological sort method
void Digraph::dfs(vertex* vcur) {
  marks.insert(vcur);
  for (const auto & adj : vcur->adjacency) {
    vertex* suc = adj.second;
    if (marks.find(suc) == marks.end()) {
      this->dfs(suc);
    } 
  }
  topo.push_front(vcur);
}

//method to calculate and print out a topological sort of the graph
void Digraph::getTopoSort(){
    marks.clear();
    topo.clear();
    for (const auto & v : work) {
        if (marks.find(v.second) == marks.end()) {
            this->dfs(v.second);
        }
    }
    // Display it
   for (const auto v : topo) {
    std::cout << v->course << "\n";
  }
}

      

        
        
        
      

    

In the last part of my implementation, I tried to do 2 things. Find the shortest path from the first vertex to all other vertices, and also find the shortest path that visits each vertex and returns to the first. I completely lost this implementation. I assumed from reading I need to use Dijkstra's algorithm to implement it. I've tried the last 3 days to no avail. Has my digraph installed a bad way to accomplish these steps? Any guidance is appreciated.