http://soj.sysu.edu.cn/show_problem.php?pid=1005&cid=1779
1 #include <bits/stdc++.h> 2 3 using namespace std; 4 5 int graph[101][101]; 6 int kind[101][101]; 7 int vis[101]; 8 int pre[101]; 9 int post[101]; 10 11 int n, m; 12 int ans=0; 13 int flag; 14 int tag; 15 16 void dfs(int x) 17 { 18 pre[x] = ++tag; 19 for(int i=1; i<=n; i++) 20 { 21 if(graph[x][i]) 22 { 23 if(pre[i] == 0) 24 { 25 kind[x][i] = 1; 26 dfs(i); 27 } 28 else 29 { 30 if(post[i] == 0) 31 { 32 kind[x][i] = 3; 33 flag=0; 34 } 35 36 else if(pre[i] > pre[x]) 37 kind[x][i] = 2; 38 else 39 kind[x][i] = 4; 40 } 41 } 42 } 43 post[x] = ++tag; 44 } 45 46 int main() 47 { 48 int ca; 49 while(cin >> n >> m) 50 { 51 tag=0; 52 flag=1; 53 memset(graph, 0, sizeof(graph)); 54 memset(vis, 0, sizeof(vis)); 55 memset(kind, 0, sizeof(kind)); 56 for(int i=0; i<m; i++) 57 { 58 int u, v; 59 cin >> u >> v; 60 graph[u][v]=1; 61 } 62 dfs(1); 63 int q; 64 cin >> q; 65 for(int i=0; i<q; i++) 66 { 67 int u, v; 68 cin >> u >> v; 69 cout << "edge (" << u << "," << v << ") is "; 70 if(kind[u][v] == 1) 71 cout << "Tree Edge" << endl; 72 if(kind[u][v] == 2) 73 cout << "Down Edge" << endl; 74 if(kind[u][v] == 3) 75 cout << "Back Edge" << endl; 76 if(kind[u][v] == 4) 77 cout << "Cross Edge" << endl; 78 } 79 } 80 return 0; 81 }