E旅行商问题

#include <bits/stdc++.h>
#define LL long long
using namespace std;
const int MAXN = 500000 + 10;
struct Edge
{
    int to, next, w;
} edge[2 * MAXN];
int tot;
int ssum=0;
int head[MAXN];
int dis[MAXN];
int N, M;
int D[MAXN];
 
void init()
{
 
    tot = 0;
    memset(head, -1, sizeof(head));
    memset(D, 0, sizeof(D));
 
}
 
void addedge(int u, int v, int w)
{
    edge[tot].to = v;
    edge[tot].next = head[u];
    edge[tot].w = w;
    head[u] = tot++;
}
 
int dfs(int u, int pre = -1)
{
 
    int ans = u;
    for(int i=head[u]; i!=-1; i=edge[i].next)
    {
        int v = edge[i].to;
        if(v == pre) continue;
        dis[v] = dis[u] + edge[i].w;
        int dv = dfs(v, u);
        if(dis[ans] < dis[dv]) ans = dv;
    }
 
    return ans;
}
 
void solve(int u)
{
    dis[u] = 0;
    u = dfs(u);
    dis[u] = 0;
    int v = dfs(u);
 
    D[1] = max(D[1], dis[1]);
    dis[v] = 0;
    dfs(v);
    D[1] = max(D[1], dis[1]);
}
 
int main()
{
 
        scanf("%d", &N);
        int u,v, w;
        init();
        for(int i=2; i<=N; i++)
        {
            scanf("%d%d%d",&u, &v, &w);
            ssum+=w;
            addedge(u, v, w);
            addedge(v, u, w);
        }
    solve(1);
    printf("%d",(ssum-D[1])*2+D[1]); 
    return 0;
 
}