Uva796 Critical Links

用tarjan缩点 
然后用dfn[u] < low[v]缩点并且保存起来 
在sort一遍输出

 #include<stdio.h>
 #include<string.h>
 #include<algorithm>

 using namespace std;

 const int maxn = ;

 struct Node {
     int u;
     int v;
     int next;
 };
 struct Edge{
     int u;
     int v;
 };
 Edge edge[maxn];
 Node node[maxn * ];
 int head[maxn];
 int dfn[maxn];
 int low[maxn];
 int fath[maxn];
 bool vis[maxn];
 bool maps[maxn][maxn];
 int n, tol, cnt;

 void init() {
     cnt = tol= ;
     memset(dfn, , sizeof(dfn));
     memset(low, , sizeof(low));
     memset(maps, , sizeof(maps));
     memset(fath, , sizeof(fath));
     memset(head, -, sizeof(head));
     memset(vis, false, sizeof(vis));
 }

 void addnode(int u, int v) {
     node[tol].u = u;
     node[tol].v = v;
     node[tol].next = head[u];
     head[u] = tol++;
 }

 void dfs(int u, int fa){
     fath[u] = fa;
     low[u] = dfn[u] = ++cnt;
     vis[u] = true;
     for(int i=head[u]; i!=-; i=node[i].next) {
         int v = node[i].v;
         if(!dfn[v]) {
             dfs(v, u);
             low[u] = min(low[u], low[v]);
         } else if(v != fa) {
             low[u] = min(low[u], dfn[v]);
         }
     }
 }

 void tarjan() {
     for(int u=; u<n; u++) {
         if(!dfn[u]) {
             dfs(u, u);
         }
     }
 }

 bool cmp(Edge a, Edge b) {
     if(a.u == b.u)
         return a.v < b.v;
     else
         return a.u < b.u;
 }

 void solve() {
     tol = ;
     for(int u=; u<n; u++) {
         int v = fath[u];
         if(low[u] > dfn[v] && v != u) {
             edge[tol].u = u;
             edge[tol].v = v;
             if(edge[tol].u > edge[tol].v)
                 swap(edge[tol].u, edge[tol].v);
             tol++;
         }
     }
     sort(edge, edge+tol, cmp);
     printf("%d critical links\n", tol);
     for(int i=; i<tol; i++) {
         printf("%d - %d\n", edge[i].u, edge[i].v);
     }
     printf("\n");
 }

 int main() {
     while(scanf("%d", &n) != EOF) {
         init();
         if(n == ) {
             printf("0 critical links\n\n");
             continue;
         }
         for(int i=; i<=n; i++) {
             int u;
             int num;
             scanf("%d (%d)", &u, &num);
             for(int j=; j<=num; j++) {
                 int v;
                 scanf("%d", &v);
                 maps[u][v] = maps[v][u] = ;
             }
         }
         for(int i=; i<n; i++) {
             for(int j=i+; j<n; j++) {
                 if(maps[i][j]) {
                     addnode(i, j);
                     addnode(j, i);
                 }
             }
         }
         tarjan();
         solve();
     }
     return ;
 }