vijos p1523 贪吃的九头龙 思考思考再思考，就荒废了4小时

树形DP要有自己的风格，转二叉树是基础，考虑边界最头疼。

 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 using namespace std;
 int point[],next[],v[],c[],cnt=,N,M,K,f[][][],d[],con[],pre[];
 int l[],r[];
 bool p[];
 void insect(int x,int y,int z){next[cnt]=point[x];point[x]=cnt;v[cnt]=y;c[cnt]=z;cnt++;}
 void dfs(int x)
 {
     int i,j=-;
     for (i=point[x];i!=-;i=next[i])
     if (p[v[i]]==)
     {
         p[v[i]]=;
         if (l[x]==) l[x]=v[i],d[v[i]]=c[i],pre[v[i]]=,j=l[x]; else
         {
             r[j]=v[i]; d[v[i]]=c[i]; pre[r[j]]=j; j=r[j];
         }
     }
     if (j==-) return;
     dfs(j); con[j]=con[l[j]]+;
     while (pre[j]!=) j=pre[j],dfs(j),con[j]=con[l[j]]+con[r[j]]+;
 }
 int dp(int x,int k,int t)
 {
     if (x==) return ;
     if (f[x][k][t]!=-) return f[x][k][t];
     int i,l1,r1,num=;
     for (i=;i<k;++i)
     if ((i<=con[l[x]])&&(k--i<=con[r[x]]))
     {
         l1=dp(l[x],i,);
         r1=dp(r[x],k--i,t);
         num=min(num,l1+r1+(t==)*d[x]);
     }
     for (i=;i<=k;++i)
     if ((i<=con[l[x]])&&(k-i<=con[r[x]]))
     {
         l1=dp(l[x],i,);
         r1=dp(r[x],k-i,t);
         num=min(num,l1+r1+(M==)*(t==)*d[x]);
     }f[x][k][t]=num;
     return num;
 }
 int main()
 {
     memset(point,-,sizeof(point));
     memset(next,-,sizeof(next));
     memset(f,-,sizeof(f));
     memset(v,,sizeof(v));
     memset(c,,sizeof(c));
     memset(p,,sizeof(p));
     scanf("%d %d %d\n",&N,&M,&K);
     if (K+M->N) {printf("-1\n");return ;}
     int i,a,b,c;
     for (i=;i<N;++i)
     {
         scanf("%d %d %d\n",&a,&b,&c);
         insect(a,b,c);insect(b,a,c);
     }p[]=; dfs();
     printf("%d\n",dp(l[],K-,));
     return ;
 }