hdu 2586 How far away ？

#include<stdio.h>
#include<iostream>
#include<algorithm>
#include<string.h>
#include<vector>
#include<queue>
using namespace std;

struct Edge{
	int v,cost;
	Edge(int _v=0,int _cost=0):v(_v),cost(_cost){
	}
};
vector<Edge> mp[40004];
int vis[40004],s,e,flag;
void addEdge(int from,int to,int cost){
	mp[from].push_back(Edge(to,cost));
	mp[to].push_back(Edge(from,cost));
}

void dfs(int t, int dis)
{
	if(mp[t].empty()) //注意判断是否为空 
		return;
	if(t == e) //到达终点
	{
		flag = 1;//找到终点 
		cout<<dis<<endl;
	}
	
	int size = mp[t].size();
	for(int j=0; j<size; j++)
	{
		if(!vis[mp[t][j].v])
		{
			vis[mp[t][j].v] = 1;
			dfs(mp[t][j].v, dis + mp[t][j].cost);
			if(flag)
				return;
			vis[mp[t][j].v] = 0;
		}
	}
}
int main(){
	
	int t;
	scanf("%d",&t);
	while(t--){		
		int n,m;
		scanf("%d%d",&n,&m);
		for(int i=0;i<n-1;i++){
			int a,b,c;
			scanf("%d%d%d",&a,&b,&c);
			addEdge(a,b,c);
		}			
		for(int i=1; i<=m; i++)
		{
			memset(vis, 0, sizeof(vis));
			flag = 0; 
			scanf("%d %d",&s,&e);
			vis[s] = 1; 
			dfs(s, 0);
		}		
		for(int i=0; i<n; i++)
		{
			mp[i].clear(); 
		}
	}
	return 0;
}