HDU 4679 Terrorist’s destroy

如果不在最长路的边，那么肯定是w*最长路。

如果在最长路，那么把最长路分成两段，左边树的最长路就是左段+左边点的次短路(不包含最长路上的点的最长路) ，右边同理。

还有就是更新，经过左端点的最长路，不一定是整颗左边树的最长路，乱搞一下就可以了。我是搞成一条链，写的很麻烦。。从一点搞到了快四点。。

 #include <iostream>
 #include <cstdio>
 #include <cstring>
 #include <cmath>
 #include <queue>
 #include <algorithm>
 using namespace std;
 #define INF 1000000
 struct node
 {
     int u,v,w,next,id;
 } edge[];
 int t,n,first[],flag[];
 int d[],in[],pre[];
 int pre1[];
 int pre2[];
 int sp1[];
 int sp2[];
 int sp3[];
 int sp4[];
 int dp[];
 int qu[];
 int qv[];
 int qw[];
 void CL()
 {
     int i;
     for(i = ; i <= n; i ++)
     {
         first[i] = -;
         flag[i] = ;
         dp[i] = ;
     }
     t = ;
 }
 void add(int u,int v,int w,int id)
 {
     edge[t].u = u;
     edge[t].v = v;
     edge[t].w = w;
     edge[t].next = first[u];
     edge[t].id = id;
     first[u] = t ++;
 }
 void dfs(int x)
 {
     int i,maxz,v;
     in[x] = ;
     maxz = ;
     for(i = first[x]; i != -; i = edge[i].next)
     {
         v = edge[i].v;
         if(flag[v]||in[v]) continue;
         in[v] = ;
         dfs(v);
         maxz =  dp[v] + ;
     }
     dp[x] = maxz;
     return;
 }
 int spfa(int x)
 {
     int u,v,i;
     for(i = ; i <= n; i ++)
     {
         d[i] = -INF;
         pre[i] = -;
         in[i] = ;
     }
     queue<int>que;
     que.push(x);
     in[x] = ;
     d[x] = ;
     while(!que.empty())
     {
         u = que.front();
         que.pop();
         for(i = first[u]; i != -; i = edge[i].next)
         {
             v = edge[i].v;
             if(in[v]) continue;
             if(d[v] < d[u] + )
             {
                 d[v] = d[u] + ;
                 pre[v] = u;
                 pre1[v] = i;
                 in[v] = ;
                 que.push(v);
             }
         }
     }
     int id,maxz = ;
     for(i = ; i <= n; i ++)
     {
         if(maxz < d[i])
         {
             maxz = d[i];
             id = i;
         }
     }
     return id;
 }
 int main()
 {
     int cas,i,u,v,w,a,b,tmax,bb,aa,sn = ;
     scanf("%d",&cas);
     while(cas--)
     {
         scanf("%d",&n);
         CL();
         for(i = ; i < n; i ++)
         {
             scanf("%d%d%d",&u,&v,&w);
             add(u,v,w,i);
             add(v,u,w,i);
             qu[i] = u;
             qv[i] = v;
             qw[i] = w;
         }
         b = spfa(a = spfa());
         bb = b;
         aa = a;
         tmax = d[b];
         while(b != a)
         {
             flag[b] = ;
             pre2[pre[b]] = b;
             b = pre[b];
         }
         flag[a] = ;
         for(i = ; i <= n; i ++)
             in[i] = ;
         for(i = ; i <= n; i ++)
         {
             if(flag[i]||in[i])
             {
                 dfs(i);
             }
         }
         int minz = INF,num,res = -;
         b = bb;
         num = ;
         while()
         {
             sp1[b] = dp[b]+tmax - num;
             sp2[b] = num + dp[b];
             num ++;
             if(a == b) break;
             b = pre[b];
         }
         int pos = ;
         b = bb;
         a = aa;
         while(b != a)
         {
             sp2[pre[b]] = max(pos,sp2[pre[b]]);
             pos = sp2[pre[b]];
             b = pre[b];
         }
         b = bb;
         a = aa;
         pos = ;
         while(a != b)
         {
             sp1[pre2[a]] = max(pos,sp1[pre2[a]]);
             pos = sp1[pre2[a]];
             a = pre2[a];
         }
         b = bb;
         a = aa;
         for(i = ; i < n; i ++)
         {
             if(flag[qu[i]]&&flag[qv[i]])
             {
                 if(pre[qu[i]] == qv[i])
                 {
                     u = qu[i];
                     v = qv[i];
                 }
                 else
                 {
                     u = qv[i];
                     v = qu[i];
                 }
                 int tt = qw[i]*(max(sp1[v],sp2[u]));
                 if(minz > tt)
                 {
                     minz = tt;
                     res = i;
                 }
                 else if(minz == tt)
                 {
                     res = min(res,i);
                 }
             }
             else
             {
                 if(minz > qw[i]*tmax)
                 {
                     minz = qw[i]*tmax;
                     res = i;
                 }
                 else if(minz == qw[i]*tmax)
                 {
                     res = min(res,i);
                 }
             }
         }
         printf("Case #%d: %d\n",sn++,res);
     }
     return ;
 }