fork download
copy 
  1. #include <bits/stdc++.h> 
  2.  
  3. using namespace std;  
  4.  
  5. typedef long long ll;  
  6. typedef pair<int, int> ii;  
  7.  
  8. const int INF = 1e9;  
  9. const ll LINF = 1e18;  
  10.  
  11. template<typename T>
  12. void minimize(T& a, const T& b) {
  13. 	if (b < a) a = b; 
  14. }
  15.  
  16. const int N = 25e2 + 5; 
  17.  
  18. int n, m;  
  19. vector<int> adj[N]; 
  20. bool vis[N]; 
  21. int level[N]; 
  22.  
  23. void bfs(int s, int& ans) {
  24. 	memset(vis, 0, sizeof vis);   
  25. 	memset(level, -1, sizeof level);  
  26.  
  27. 	queue<int> q;  
  28. 	vis[s] = true;  
  29. 	level[s] = 0;    
  30. 	q.push(s); 
  31.  
  32. 	while (!q.empty()) {
  33. 		int u = q.front(); q.pop();  
  34.  
  35. 		for (int v : adj[u]) {
  36. 			if (!vis[v]) {
  37. 				vis[v] = true; 
  38. 				level[v] = level[u] + 1; 
  39. 				q.push(v); 
  40. 			}
  41. 			else if (level[v] >= level[u]) {// (level[u] == level[v] || level[u] + 1 == level[v]) 
  42. 				int cycle_len = level[u] + 1 + level[v]; // s -> u -> v -> s
  43. 				minimize(ans, cycle_len); 
  44. 			}
  45. 		}
  46. 	}
  47. }
  48.  
  49. int main() {
  50. 	ios::sync_with_stdio(false); 
  51. 	cin.tie(nullptr); 	
  52. 	cin >> n >> m; 
  53. 	for (int i = 0; i < m; i++) {
  54. 		int u, v; 
  55. 		cin >> u >> v; 
  56. 		adj[u].push_back(v); 
  57. 		adj[v].push_back(u); 
  58. 	}
  59.  
  60. 	// Với mỗi đỉnh s từ 1 đến n ta tìm chu trình ngắn nhất đi qua s
  61. 	int ans = INF; 
  62. 	for (int s = 1; s <= n; s++) bfs(s, ans);
  63.  
  64. 	if (ans == INF) ans = -1;  
  65. 	cout << ans << '\n'; 
  66. }
Success #stdin #stdout 0s 5284KB
comments (?)
stdin
copy 
5 6
1 2
1 3
2 4
2 5
3 4
4 5
stdout
copy 
3
https://ideone.com/1LgoDh
language:
C++14 (gcc 8.3)
created:
291 days ago
visibility:
secret

Share or Embed source code

Discover > Sphere Engine API

The brand new service which powers Ideone!

Discover > IDE Widget

Widget for compiling and running the source code in a web browser!