1 #include<iostream>
 2 #include<memory.h>
 3 #include<stack>
 4 
 5 using namespace std;
 6 
 7 bool paths[101][101];
 8 int visited[101];
 9 bool isDAG;
10 int vertices,edges;
11 
12 void DFS(int current){
13     for(int j =1; isDAG == true && j <=vertices; j++){
14         if(paths[current][j] == true){
15             if(visited[j] == 0){
16                 visited[j] = 1;
17                 DFS(j);
18             }
19             else if(visited[j] == 1)
20                 isDAG = false;
21         }
22     }
23     //marked node as visted one stoping duplicated visiting when other visit trying to visit this pre-visit node
24     visited[current] = -1;
25 }
26 int main(){
27     int from,dest;
28     memset(paths,false,sizeof(paths));
29     memset(visited,0,sizeof(visited));
30     cin >> vertices >> edges;
31     for(int i=1;i<= edges;i++){
32         cin >> from >> dest;
33         paths[from][dest] = true;
34     }
35     //depth-first search checking every node
36     isDAG = true;
37     for(int i=1; isDAG == true && i <= vertices; i++){
38         if(visited[i] == 0){
39             visited[i] == 1;
40             DFS(i);
41         }
42     }
43     if(isDAG)
44         cout << 1 << endl;
45     else
46         cout << 0 << endl;
47     return 0;
48 }