58pts求调

#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N=5e5+5;
struct _{
	int v,w;
};
vector<_> a[N];
int n,s,dp[N],vis[N];
int ans;
void dfs(int u){
	vis[u]=1;
	int aaaa=0;
	for(int i=0;i<a[u].size();i++){
		int v=a[u][i].v;
		int w=a[u][i].w;
		if(!vis[v]){
			dfs(v);
			aaaa=max(aaaa,dp[v]+w);
		}
	}
	for(int i=0;i<a[u].size();i++){
		int v=a[u][i].v;
		int w=a[u][i].w;
		if(!vis[v]){
			ans+=aaaa-dp[v]-w;
		}
	}
	vis[u]=0;
	dp[u]=aaaa;
}
signed main(){
	cin>>n>>s;
	for(int i=1;i<=n;i++){
		int u,v,w;
		cin>>u>>v>>w;
		a[u].push_back({v,w});
		a[v].push_back({u,w});
	}
	dfs(s);
	cout<<ans<<endl;
}