dataStructure@ Check if a directed graph has cycles

 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include<limits>
 #include<vector>
 using namespace std;
 const int maxn = ;
 struct edge{
     int to, cost;
     edge(int t){
         this->to = t; this->cost = ;
     }
 };
 void addEdge(vector<edge> &edgelist, vector<vector<int> > &G, int from, int to){
     edgelist.push_back(edge(to));
     G[from].push_back(edgelist.size()-);
 }
 void addDoubleEdge(vector<edge> &edgelist, vector<vector<int> > &G, int from, int to){
     addEdge(edgelist,G,from,to);
     addEdge(edgelist,G,to,from);
 }
 bool isCyclic(vector<edge> edgelist, vector<vector<int> > G,vector<bool> vis, vector<bool> RecStack, int v){
     for(int i=;i<G[v].size();++i){
         edge e = edgelist[G[v][i]];
         if(RecStack[e.to]) return true;
         if(!vis[e.to]){
             vis[e.to] = true; RecStack[e.to] = true;
             if(isCyclic(edgelist,G,vis,RecStack,e.to)) return true;
             RecStack[e.to] = false;
         }
     }
     return false;
 }
 void buildMap(vector<edge> &edgelist, vector<vector<int> > &G){
     addEdge(edgelist,G,,);
     addEdge(edgelist,G,,);
     addEdge(edgelist,G,,);
     addEdge(edgelist,G,,);
     addEdge(edgelist,G,,);
     addEdge(edgelist,G,,);
 }
 int main(){
     vector<edge> edgelist;
     vector<vector<int> > G(maxn);
     vector<bool> vis(maxn);
     vector<bool> RecStack(maxn);

     buildMap(edgelist,G);

     for(int i=;i<vis.size();++i) vis[i]=false;
     for(int i=;i<RecStack.size();++i) RecStack[i]=false;

     for(int i=;i<G.size();++i){
         if(!vis[i]){
             vis[i] = true; RecStack[i] = true;
             if(isCyclic(edgelist,G,vis,RecStack,i)){
                 cout<<i<<" starts a cycle"<<endl;
             }
             RecStack[i] = false;
         }
     }

     return ;
 }