HDU 4738 双连通分量 Caocao's Bridges

求权值最小的桥，考虑几种特殊情况：

• 图本身不连通，那么就不用派人去了
• 图的边双连通分量只有一个，答案是-1
• 桥的最小权值是0，但是也要派一个人过去

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

 const int maxn =  + ;
 const int maxm =  + ;

 int n, m;

 int cc;
 int pa[maxn];
 int findset(int x) { return x == pa[x] ? x : pa[x] = findset(pa[x]); }

 void Union(int x, int y)
 {
     int px = findset(x), py = findset(y);
     if(px != py) { pa[px] = py; cc--; }
 }

 struct Edge
 {
     int v, nxt, w;
 }edges[maxm * ];
 int ecnt;
 int head[maxn];

 void AddEdge(int u, int v, int d)
 {
     edges[ecnt].v = v;
     edges[ecnt].w = d;
     edges[ecnt].nxt = head[u];
     head[u] = ecnt++;
 }

 stack<int> S;
 bool isbridge[maxm * ];
 int dfs_clock, scc_cnt;
 int low[maxn], pre[maxn], sccno[maxn];

 void dfs(int u, int fa)
 {
     pre[u] = low[u] = ++dfs_clock;
     S.push(u);

     for(int i = head[u]; ~i; i = edges[i].nxt)
     {
         if(i == (fa ^ )) continue;
         int v = edges[i].v;
         if(!pre[v])
         {
             dfs(v, i);
             low[u] = min(low[u], low[v]);
             if(low[v] > low[u]) isbridge[i] = true;
         }
         else if(!sccno[v]) low[u] = min(low[u], pre[v]);
     }

     if(low[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(isbridge, false, sizeof(isbridge));
     memset(pre, , sizeof(pre));
     memset(sccno, , sizeof(sccno));
     for(int i = ; i <= n; i++) if(!pre[i]) dfs(i, -);
 }

 int main()
 {
     while(scanf("%d%d", &n, &m) ==  && n)
     {
         ecnt = ;
         memset(head, -, sizeof(head));
         cc = n;
         for(int i = ; i <= n; i++) pa[i] = i;
         while(m--)
         {
             int u, v, d; scanf("%d%d%d", &u, &v, &d);
             Union(u, v);
             AddEdge(u, v, d); AddEdge(v, u, d);
         }

         if(cc > ) { puts(""); continue; }

         find_scc();

         if(scc_cnt == ) { puts("-1"); continue; }

         int ans = ;
         for(int i = ; i < ecnt; i += ) if(isbridge[i]) ans = min(ans, edges[i].w);
         if(!ans) ans = ;
         printf("%d\n", ans);
     }

     return ;
 }

代码君