注意点：
- 该题存在点权，初始化时应当设置siz[i]=w[i].
#include<cstdio>
#include<iostream>
#define ll long long
using namespace std;
const int MAXN=1e3,MAXM=2*MAXN,INF=2e9;
struct Edge{
int from,to,nxt;
}e[MAXM];
int head[MAXN],edgeCnt=1;
void addEdge(int u,int v){
e[++edgeCnt].from=u;
e[edgeCnt].to=v;
e[edgeCnt].nxt=head[u];
head[u]=edgeCnt;
}
int w[MAXN];//居民人口数
int siz[MAXN],dep[MAXN];
ll f[MAXN];//重心
void dfs_init(int x,int in_edge){
siz[x]=w[x];
for(int i=head[x];i;i=e[i].nxt){
if(i==(in_edge^1))continue;
int nowV=e[i].to;
dep[nowV]=dep[x]+1;
dfs_init(nowV,i);
siz[x]+=siz[nowV];
}
f[1]+=w[x]*dep[x];
}
void dfs(int x,int in_edge){
for(int i=head[x];i;i=e[i].nxt){
if(i==(in_edge^1))continue;
int nowV=e[i].to;
f[nowV]=f[x]+siz[1]-2*siz[nowV];
dfs(nowV,i);
}
}
int main(){
int n;
scanf("%d",&n);
for(int i=1;i<=n;i++){
scanf("%d",&w[i]);
int a,b;
scanf("%d%d",&a,&b);
if(a){
addEdge(i,a);
addEdge(a,i);
}
if(b){
addEdge(i,b);
addEdge(b,i);
}
}
dfs_init(1,0);
dfs(1,0);
ll ans=INF;
for(int i=1;i<=n;i++){
ans=min(ans,f[i]);
}
printf("%lld
",ans);
return 0;
}