HDU 4738 Caocao's Bridges(Tarjan)

题目链接

 #include <iostream>
 #include <cstring>
 #include <cstdio>
 #include <queue>
 #include <cstdlib>
 using namespace std;
 #define N 1001
 #define M 20000001
 #define INF 0x3f3f3f3f
 struct node
 {
     int u,v,next;
 }edge[M];
 int first[N],DFN[N],Belong[N],stack[N],Low[N],cnum[N];
 int in[N],d[N];
 int qu[M],qv[M],qw[M];
 int n,m;
 bool vis[M];
 int tot,scnt,top;
 int o[M];
 void CL()
 {
     tot = scnt = top = ;
     memset(first,-,sizeof(first));
     memset(in,,sizeof(in));
     memset(DFN,,sizeof(DFN));
     memset(vis,,sizeof(vis));
 }
 void add(int u,int v,int w)
 {
     edge[tot].u = u;
     edge[tot].v = v;
     edge[tot].next = first[u];
     first[u] = tot ++;
 }
 void Tarjan(int u)
 {
     int v,i;
     DFN[u] = Low[u] = ++ tot;
     stack[top++] = u;
     in[u] = ;
     for(i = first[u];i != -;i = edge[i].next)
     {
         v = edge[i].v;
         if(vis[i]) continue;
         vis[i] = vis[i^] = ;
         if(!DFN[v])
         {
             Tarjan(v);
             Low[u] = min(Low[u],Low[v]);
         }
         else
         {
             Low[u] = min(Low[u],DFN[v]);
         }
     }
     if(DFN[u] == Low[u])
     {
         scnt ++;
         do
         {
             v = stack[--top];
             Belong[v] = scnt;
             in[v] = ;
             cnum[scnt] ++;
         }while(u != v);
     }
 }
 int find(int x)
 {
     int r,t;
     r = x;
     while(o[x] != x)
     x = o[x];
     while(r != x)
     {
         t = o[r];
         o[r] = x;
         r = t;
     }
     return x;
 }
 void merge(int x,int y)
 {
     x = find(x);
     y = find(y);
     if(x != y)
     o[x] = y;
 }
 int main()
 {
     int n,m,i,u,v,w,minz;
     while(scanf("%d%d",&n,&m)!=EOF)
     {
         if(n == &&m == ) break;
         CL();
         for(i = ;i <= n;i ++)
         {
             o[i] = i;
         }
         for(i = ;i < m;i ++)
         {
             scanf("%d%d%d",&u,&v,&w);
             qu[i] = u;
             qv[i] = v;
             qw[i] = w;
             merge(u,v);
             add(u,v,w);
             add(v,u,w);
         }
         int fa = find();
         for(i = ;i <= n;i ++)
         {
             if(find(i) != fa)
             break;
         }
         if(i != n+)
         {
             printf("0\n");
             continue;
         }
         minz = ;
         Tarjan();
         for(i = ;i < m;i ++)
         {
             if(Belong[qu[i]] != Belong[qv[i]])
             {
                 minz = min(minz,qw[i]);
             }
         }
         if(scnt == )
         printf("-1\n");
         else
         {
             if(minz == )
             printf("1\n");
             else
             printf("%d\n",minz);
         }
     }

 }