URAL 1039 Anniversary Party 树形dp

const int maxn=10000;
const int maxm=110000;
int n;

struct EdgeNode{
int to,next;
}edges[maxm];
int head[maxn],edge;
void init(){
memset(head,-1,sizeof(head));
edge=0;
}
void addedge(int u,int v){
edges[edge].to=v,edges[edge].next=head[u],head[u]=edge++;
}
int a[maxn];
int f[maxn][2];
int id[maxn];
int dfs(int u,int flag){
if (f[u][flag]!=-1) return f[u][flag];
int res;
if (flag){
res=0;
for (int i=head[u];i!=-1;i=edges[i].next){
int v=edges[i].to;
res+=dfs(v,0);
}
}
else{
int res1=0,res2=0;
for (int i=head[u];i!=-1;i=edges[i].next){
int v=edges[i].to;
res1+=dfs(v,1);
}
for (int i=head[u];i!=-1;i=edges[i].next){
int v=edges[i].to;
res2+=dfs(v,0);
}
res=max(res1+a[u],res2);
}
return f[u][flag]=res;
}
int main(){
while (~scanf("%d",&n)){
init();
memset(f,-1,sizeof(f));
memset(id,0,sizeof(id));
for (int i=1;i<=n;i++) scanf("%d",&a[i]);
int x,y;
while (~scanf("%d%d",&x,&y)){
if (x==0&&y==0) break;
addedge(y,x);
id[x]++;
}
int rt=1;
for (int i=1;i<=n;i++){
if (id[i]==0) rt=i;
}
printf("%d\n",dfs(rt,0));
}
return 0;
}