Detect cycle in a directed graph

// { Driver Code Starts
#include <bits/stdc++.h>
using namespace std;


 // } Driver Code Ends
/*  Function to check if the given graph contains cycle
*   V: number of vertices
*   adj[]: representation of graph
*/
bool isCyclic_util(vector<int> adj[], vector<bool> visited, int curr)
{
    if(visited[curr]==true)
        return true;
    
    visited[curr] = true;
    bool FLAG = false;
    for(int i=0;i<adj[curr].size();++i)
    {
        FLAG = isCyclic_util(adj, visited, adj[curr][i]);
        if(FLAG==true)
            return true;
    }
    return false;
}

bool isCyclic(int V, vector<int> adj[])
{
   vector<bool> visited(V,false);
   bool FLAG = false;
   for(int i=0;i<V;++i)
   {
           visited[i] = true;
           for(int j=0;j<adj[i].size();++j)
           {
               FLAG = isCyclic_util(adj,visited,adj[i][j]);
               if(FLAG==true)
                   return true;
           }
           visited[i] = false;
   }
   return false;
}

// { Driver Code Starts.

int main() {
	
	int t;
	cin >> t;
	
	while(t--){
	    
	    int v, e;
	    cin >> v >> e;
	    
	    vector<int> adj[v];
	    
	    for(int i =0;i<e;i++){
	        int u, v;
	        cin >> u >> v;
	        adj[u].push_back(v);
	    }
	    
	    cout << isCyclic(v, adj) << endl;
	    
	}
	
	return 0;
}  // } Driver Code Ends

We can just use the logic of back edge which will be O(V+E)