connected components of triangle faces in a mesh - graph

Question

I have a list of vertices and faces which index the vertex:
For example the list of vertices are (x,y,z) :
0 1 0
1 1 1
2 0 1
3 0 0
1 1 2
...
...
...
Faces that index the vertex:
0 1 2
2 3 4
4 0 1
...
...
...
With the list of faces I need to group them up for those that faces are connected to each other. For the first 3 faces I know that they are connected to each other as they have common index. How do I implement an algorithm to do this? thanks.
I use the method from this link using depth first search to visit all the node but gets a segmentation fault inside the class
https://www.geeksforgeeks.org/depth-first-search-or-dfs-for-a-graph/
#include <bits/stdc++.h>
using namespace std;
class Graph {
// A function used by DFS
void DFSUtil(int v);
public:
int count;
map<int, bool> visited;
map<int, list<int> > adj;
// function to add an edge to graph
void addEdge(int v, int w);
// prints DFS traversal of the complete graph
void DFS();
};
void Graph::addEdge(int v, int w)
{
adj[v].push_back(w); // Add w to v’s list.
}
void Graph::DFSUtil(int v)
{
// Mark the current node as visited and print it
visited[v] = true;
cout << v << " ";
// Recur for all the vertices adjacent to this vertex
list<int>::iterator i;
for (i = adj[v].begin(); i != adj[v].end(); ++i)
if (!visited[*i])
DFSUtil(*i);
}
// The function to do DFS traversal. It uses recursive
// DFSUtil()
void Graph::DFS()
{
count = 0;
// Call the recursive helper function to print DFS
// traversal starting from all vertices one by one
for (auto i : adj)
if (visited[i.first] == false)
{
DFSUtil(i.first);
count++;
}
}
int main()
{
// Create a graph given in the above diagram
Graph g;
for face in faces :
{
g.addEdge(face[0], face[1]);
g.addEdge(face[0], face[2]);
g.addEdge(face[1], face[0]);
g.addEdge(face[1], face[2]);
g.addEdge(face[2], face[0]);
g.addEdge(face[2], face[1]);
}
cout << "Following is Depth First Traversal \n";
// Function call
g.DFS();
cout << "number of connected components = " << g.count << "\n";
return 0;
}