Detect Cycle In Directed/Undirected Graph

#include <iostream>
#include <vector>
#include <list>
#include <unordered_set>
using namespace std;

class DirectedGraph{
    int n; // # of nodes
    vector<list<int>> adj; // adjacency lists
public:
    DirectedGraph(int N):n(N),adj(N,list<int>()){};
    void addEdge(int u, int v){ // to add an edge u->v to graph
        adj[u].push_back(v);
    }
    bool isCyclic(){
        //If has back edge, then has cycle
        vector<bool> visited(n,false);
        unordered_set<int> recStack; // recursion stack
        
        for (int i=0;i<n;++i){
            if (dfs(i,visited,recStack)) 
                return true;
        }
        return false;
    }
    
    bool dfs(int i, vector<bool> &visited, unordered_set<int> &recStack){
        if (recStack.count(i)) return true;
        if (visited[i]) return false;
        
        visited[i] = true;
        recStack.insert(i);
        for (auto x:adj[i])
            if (dfs(x,visited,recStack))
                return true;
        
        recStack.erase(i);
        return false;
    }
};


int main() {
    DirectedGraph g(4);
    g.addEdge(0, 1); 
    //g.addEdge(0, 2); 
    g.addEdge(1, 2); 
    //g.addEdge(2, 0); 
    g.addEdge(2, 3); 
    //g.addEdge(3, 3); 
    cout << g.isCyclic();
    return 0;
}