HDU 3072 SCC Intelligence System

给出一个带权有向图，要使整个图连通。SCC中的点之间花费为0，所以就先缩点，然后缩点后两点之间的权值为最小边的权值，把这些权值累加起来就是答案。

 #include <iostream>
 #include <cstdio>
 #include <algorithm>
 #include <cstring>
 #include <vector>
 #include <stack>
 using namespace std;

 int n, m;

 const int maxn =  + ;

 vector<int> G[maxn], C[maxn];

 stack<int> S;
 int pre[maxn], lowlink[maxn], sccno[maxn];
 int dfs_clock, scc_cnt;

 void dfs(int u)
 {
     pre[u] = lowlink[u] = ++dfs_clock;
     S.push(u);
     for(int i = ; i < G[u].size(); i++)
     {
         int v = G[u][i];
         if(!pre[v])
         {
             dfs(v);
             lowlink[u] = min(lowlink[u], lowlink[v]);
         }
         else if(!sccno[v]) lowlink[u] = min(lowlink[u], pre[v]);
     }

     if(lowlink[u] == pre[u])
     {
         scc_cnt++;
         for(;;)
         {
             int x = S.top(); S.pop();
             sccno[x] = scc_cnt;
             if(x == u) break;
         }
     }
 }

 void find_scc()
 {
     dfs_clock = scc_cnt = ;
     memset(pre, , sizeof(pre));
     memset(sccno, , sizeof(sccno));
     for(int i = ; i < n; i++) if(!pre[i]) dfs(i);
 }

 int cost[maxn];

 int main()
 {
     while(scanf("%d%d", &n, &m) == )
     {
         for(int i = ; i < n; i++) { G[i].clear(); C[i].clear(); }
         while(m--)
         {
             int u, v, d; scanf("%d%d%d", &u, &v, &d);
             G[u].push_back(v); C[u].push_back(d);
         }
         find_scc();

         memset(cost, -, sizeof(cost));
         for(int i = ; i < n; i++)
             for(int j = ; j < G[i].size(); j++)
             {
                 int u = sccno[i], v = sccno[G[i][j]];
                 if(u == v) continue;
                 if(cost[v] == -) cost[v] = C[i][j];
                 else cost[v] = min(cost[v], C[i][j]);
             }

         int ans = ;
         for(int i = ; i <= scc_cnt; i++) if(cost[i] != -) ans += cost[i];
         printf("%d\n", ans);
     }

     return ;
 }

代码君