codevs 1378选课 树形DP

 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 using namespace std;
 int N,M,tl[],tr[],f[][],num[],con[];
 void insect(int fa,int now)
 {
     if (tl[fa]==)
      {tl[fa]=now;}
     else
      {
          int i=tl[fa];
          while (tr[i]!=) i=tr[i];
          tr[i]=now;
      }
 }
 void dfs(int x)
 {
     if (tr[x]!=) dfs(tr[x]);
     if (tl[x]!=) dfs(tl[x]);
     con[x]=con[tr[x]]+con[tl[x]]+;
     int i,j;
     f[x][]=num[x];
     for (i=;i<=con[tr[x]];++i)
     {
         f[x][i]=max(f[x][i],f[tr[x]][i]);
         for (j=;j<=con[tl[x]];++j)
          f[x][i+j+]=max(f[x][i+j+],num[x]+f[tr[x]][i]+f[tl[x]][j]);
     }
 }
 int main()
 {
     memset(f,,sizeof(f));
     memset(tl,,sizeof(tl));
     memset(tr,,sizeof(tr));
     memset(con,,sizeof(con));
     memset(num,,sizeof(num));
     scanf("%d %d\n",&N,&M);
     int i,j,x,y;
     for (i=;i<=N;++i)
     {
         scanf("%d %d\n",&x,&num[i]);
         insect(x,i);
     }
     dfs(tl[]);
     printf("%d\n",f[tl[]][M]);
 }