易错点：
- 注意预处理时的边界条件（if(degree[y]==1)D[x]+=e[i].w;else D[x]+=min(D[y],e[i].w);）.
- 笔者由于边数组开了3e5而调试了近半个小时.
#include<cstdio>
#include<iostream>
#include<cstring>
using namespace std;
const int MAXN=4e5+10,INF=1<<30;
struct Edge{
int from,to,w,nxt;
}e[MAXN];
int edgeCnt=1,head[MAXN];
void addEdge(int x,int y,int w){
e[++edgeCnt].from=x;
e[edgeCnt].to=y;
e[edgeCnt].w=w;
e[edgeCnt].nxt=head[x];
head[x]=edgeCnt;
}
int D[MAXN],degree[MAXN];
bool vis1[MAXN];
int f[MAXN];
void dfs(int x){
vis1[x]=1;
for(int i=head[x];i;i=e[i].nxt){
int y=e[i].to;
if(vis1[y])continue;
dfs(y);
if(degree[y]==1)D[x]+=e[i].w;
else D[x]+=min(D[y],e[i].w);
}
}
int ans=-INF;
bool vis2[MAXN];
void dp(int x){
vis2[x]=1;
ans=max(ans,f[x]);
for(int i=head[x];i;i=e[i].nxt){
int y=e[i].to;
if(f[y]||vis2[y])continue;
f[y]=D[y]+min(e[i].w,f[x]-min(e[i].w,D[i]));
dp(y);
}
}
int n;
void init(){
edgeCnt=1;
ans=-INF;
for(int i=1;i<=n;i++){
head[i]=vis1[i]=vis2[i]=degree[i]=f[i]=D[i]=0;
}
}
int main(){
int t;
scanf("%d",&t);
while(t--){
scanf("%d",&n);
init();
for(int i=1;i<=n-1;i++){
int x,y,z;
scanf("%d%d%d",&x,&y,&z);
addEdge(x,y,z);
addEdge(y,x,z);
degree[x]++,degree[y]++;
}
dfs(1);
f[1]=D[1];
dp(1);
printf("%d
",ans);
}
return 0;
}