这道题数据过水

#include<bits/stdc++.h>
using namespace std;
#define IL inline
#define RG register
#define gi getint()
#define gc getchar()
#define File(a) freopen(a".in","r",stdin);freopen(a".out","w",stdout)
IL int getint()
{
    RG int xi=0;
    RG char ch=gc;
    bool f=0;
    while(ch<'0'|ch>'9')ch=='-'?f=1:f,ch=gc;
    while(ch>='0'&ch<='9')xi=(xi<<1)+(xi<<3)+ch-48,ch=gc;
    return f?-xi:xi;
}
IL void pi(int k,char ch=0)
{
    if(k<0)k=-k,putchar('-');
    if(k>=10)pi(k/10,0);
    putchar(k%10+'0');
    if(ch)putchar(ch);
}
IL unsigned int LOG2(unsigned int x)
{
    unsigned int ret;
    __asm__ __volatile__ ("bsrl %1, %%eax":"=a"(ret):"m"(x));
    return ret;
}
const int MAX=1e6+7;
struct E{
    int v,next,w;
}e[MAX<<1|1];
int n,s,f[MAX],cnt,head[MAX];
long long ans;
void add(int u,int v,int w)
{
    e[++cnt]=(E){v,head[u],w};
    head[u]=cnt;
}
void dfs(int p,int fa)
{
    for(int i=head[p];~i;i=e[i].next)
      if(e[i].v!=fa)
        dfs(e[i].v,p);
    for(int i=head[p];~i;i=e[i].next)
      if(e[i].v!=fa)
        f[p]=max(f[p],e[i].w);
    for(int i=head[p];~i;i=e[i].next)
      if(e[i].v!=fa)ans+=f[p]-e[i].w;
    for(int i=head[fa];i;i=e[i].next)
      if(e[i].v==p)e[i].w+=f[p];
}
int main(void)
{
    memset(head,-1,sizeof(head));
    n=gi,s=gi;
    for(int i=1;i<n;i++)
    {
        int u=gi,v=gi,w=gi;
        add(u,v,w),add(v,u,w);
    }
    dfs(s,0);
    printf("%lld\n",ans);
    return 0;
}

for(int i=head[fa];i;i=e[i].next)
      if(e[i].v==p)e[i].w+=f[p];