poj3114Countries in War（缩点+DIJK）

http://poj.org/problem?id=3114

缩点+DIJK 注意缩点之后有重边啊 floyd会TLE

 #include <iostream>
 #include<cstring>
 #include<cstdio>
 #include<stdlib.h>
 #include<algorithm>
 #include<stack>
 #define N 510
 #define M 301000
 #define INF 0xfffffff
 using namespace std;
 struct node
 {
     int u,v,next,w;
 }edge[M];
 int t,low[N],pre[N],sccno[N],head[N],scc,dep,ww[N][N],vis[N],dis[N];
 int o[N][N];
 void init()
 {
     t = ;
     memset(head,-,sizeof(head));
 }
 void add(int u,int v,int w)
 {
     edge[t].u  =u;
     edge[t].v = v;
     edge[t].w = w;
     edge[t].next = head[u];
     head[u] = t++;
 }
 stack<int>s;
 void dfs(int u)
 {
     low[u] = pre[u] = ++dep;
     s.push(u);
     for(int i = head[u] ; i!=- ; i = edge[i].next)
     {
         int v = edge[i].v;
         if(!pre[v])
         {
             dfs(v);
             low[u] = min(low[u],low[v]);
         }
         else if(!sccno[v])
         low[u] = min(low[u],pre[v]);
     }
     if(low[u]==pre[u])
     {
         scc++;
         for(;;)
         {
             int x = s.top();s.pop();
             sccno[x] = scc;
             if(x==u)break;
         }
     }
 }
 void find_scc(int n)
 {
     scc=;dep=;
     memset(low,,sizeof(low));
     memset(pre,,sizeof(pre));
     memset(sccno,,sizeof(sccno));
     for(int i = ; i <= n ; i++)
     if(!pre[i])
     dfs(i);
 }
 int dijk(int st,int en,int n)
 {
     int i,j,k,mi;
     memset(vis,,sizeof(vis));
     for(i = ; i <= n ; i++)
     dis[i] = o[st][i];
     dis[st] = ;
     for(i =  ;i <= n ; i++)
     {
         mi = INF;
         for(j = ; j <= n ; j++)
             if(!vis[j]&&dis[j]<=mi)
             mi = dis[k=j];
         vis[k] = ;
         for(j = ; j <= n ; j++)
         if(dis[j]>o[k][j]+dis[k])
         dis[j] = o[k][j]+dis[k];
     }
     return dis[en];
 }
 int main()
 {
     int i,j,n,m,k,a,b,c,g;
     while(cin>>n>>m)
     {
         if(n==&&m==)
         break;
         memset(ww,,sizeof(ww));
         init();
         for(i =; i <= m ;i++)
         {
             scanf("%d%d%d",&a,&b,&c);
             add(a,b,c);
         }
         find_scc(n);
         for(i = ; i <= n ; i++)
            for(j = ; j <= n ;j++)
              o[i][j] = INF;
         for(i = ; i <= scc ; i++)
         o[i][i] = ;
         for(i = ; i < t ; i++)
         {
             int u = edge[i].u,v = edge[i].v;
             if(sccno[u]!=sccno[v])
             {
                 o[sccno[u]][sccno[v]] = min(o[sccno[u]][sccno[v]],edge[i].w);//没算重的之前 WA惨了
             }
         }
         scanf("%d",&k);
         while(k--)
         {
             scanf("%d%d",&a,&b);
             int xx = dijk(sccno[a],sccno[b],scc);
             if(xx==INF)
             printf("Nao e possivel entregar a carta\n");
             else
             cout<<xx<<endl;
         }
         puts("");
     }
     return ;
 }