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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4.  
  5. int bfs(vector <int>adj[],int start,int n)
  6. {
  7. 	bool visited[n+1];
  8. 	memset(visited,0,sizeof(visited));
  9. 	queue <int>q;
  10. 	q.push(start);
  11. 	int node,count=0;
  12. 	while(!q.empty())
  13. 	{
  14. 		node=q.front();
  15. 		q.pop();
  16. 		visited[node]=1;
  17. 		for(int i=0;i<adj[node].size();i++)
  18. 		{
  19. 			if(visited[adj[node][i]])return 0;
  20. 			else
  21. 			{
  22. 				q.push(adj[node][i]);
  23. 			}
  24. 		}
  25. 		count++;
  26. 	}
  27. 	if(count!=n)return 0;
  28. 	else return 1;
  29. }
  30.  
  31.  
  32. int main() {
  33.  
  34. int n,e,u,v;
  35. cin>>n>>e;
  36. vector <int>adj[n+1];
  37. for(int i=0;i<e;i++)
  38. {
  39. 	cin>>u>>v;
  40. 	adj[u].push_back(v);
  41. }
  42.  
  43. if(bfs(adj,1,n))
  44. {
  45. 	cout<<"YES"<<endl;
  46. }
  47. else
  48. cout<<"NO"<<endl;
  49.  
  50.  
  51. 	return 0;
  52. }
Success #stdin #stdout 0s 15240KB
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YES
https://ideone.com/kvIgeu
language:
C++14 (gcc 8.3)
created:
6 years ago
visibility:
public

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