树上dp，样例过了，测试点全WA，在此求助！

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N=5e5+10;
ll max_dis,ans;
ll dis[N],book[N],lvs[N];
struct T {
	ll node,edge;
}temp;
vector <T> G[N];
void find_maxdis(int step){
    book[step]=1;
    max_dis=max(max_dis,dis[step]);
    for(int i=0;i<G[step].size();i++)
        if(book[G[step][i].node]==0)
            book[G[step][i].node]=1,
            dis[G[step][i].node]=dis[step]+G[step][i].edge,
            find_maxdis(G[step][i].node);
}
void book_leaves(int step){
    bool flag=true;
    book[step]=1;
    for(int i=0;i<G[step].size();i++)
        if(book[G[step][i].node]==0) 
            flag=false,
            book_leaves(G[step][i].node);
    if(flag) lvs[step]=1;
}
ll program(int step){
    book[step]=1;
    ll max_len=0;
    for(int i=0;i<G[step].size();i++)
    	if(book[G[step][i].node]==0)
        	max_len=max(max_len,(lvs[G[step][i].node]==0?program(G[step][i].node):G[step][i].edge));
    for(int i=0;i<G[step].size();i++)
		if(book[G[step][i].node]==0){
        	ans+=max_len-G[step][i].edge;
        	G[step][i].edge=max_len;
    	}
    return max_len;
}
int main()
{
	ll n,S,u,v,w;
	cin>>n>>S;
	for(int i=1;i<=n-1;i++){
		cin>>u>>v>>w;
		temp.node=v,temp.edge=w; G[u].push_back(temp);
		temp.node=u,temp.edge=w; G[v].push_back(temp);
	}
	memset(book,0,sizeof(book));
	find_maxdis(S);
	memset(book,0,sizeof(book));
	book_leaves(S);
	memset(book,0,sizeof(book));
	program(S);
	cout<<ans<<endl;
	return 0;
}

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