CODEVS1380 没有上司的舞会 （树形DP）

f[i,0] 表示 第i个人不参加舞会 

f[i,1] 表示 第i个人参加舞会

f[i,1]=sigma(f[j,0])+v[i]   j 为 i 的孩子

f[i,1]=sigma(max(f[j,0],f[j,1]))   j 为 i 的孩子

ans=max(f[root,0],f[root,1])

Program CODEVS1380;
type arr=record
        u,v,next:longint;
    end;
const maxn=10000;
var eg:array[0..maxn] of arr;
    last:array[0..maxn] of longint;
    a:array[0..maxn] of longint;
    f:array[0..maxn,0..1] of longint;
    fa:array[0..maxn] of longint;
    i,n,u,v,j,root:longint;
procedure add(u,v:longint);
begin
  inc(j);
  eg[j].u:=u;
  eg[j].v:=v;
  eg[j].next:=last[u];
  last[u]:=j;
end;
function max(a,b:longint):longint;
begin
  if a>b then exit(a) else exit(b);
end;
procedure dfs(u:longint);
var i,v,sum1,sum2:longint;
begin
  if last[u]=-1 then
    begin
      f[u,0]:=0;
      f[u,1]:=a[u];    
      exit;
    end;
  i:=last[u]; sum1:=0; sum2:=0;
  while i<>-1 do
    begin
      v:=eg[i].v;
      dfs(v);
      sum1:=sum1+f[v,0];
      sum2:=sum2+max(f[v,0],f[v,1]);
      i:=eg[i].next;
    end;
  f[u,0]:=sum2;
  f[u,1]:=sum1+a[u];
end;
begin
  readln(n);
  j:=-1;
  for i:=1 to maxn do last[i]:=-1;
  for i:=1 to n do readln(a[i]);
  readln(v,u);
  while (v<>0) and (u<>0) do
    begin
      fa[v]:=u;
      add(u,v);
      readln(v,u);
    end;
  for i:=1 to n do if fa[i]=0 then root:=i;
  dfs(root);  
  writeln(max(f[root,0],f[root,1]));
end.