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\n",ans);
    }
    return 0;
}