dfs，3个wa，剩下的tle

#include<bits/stdc++.h>
#define int long long
using namespace std;
struct bian{
	int s,e,w;
} b[100002];
int n,m;
bool flag=false;
bool vis[100002]={false};
void dfs(int now,int end,int val){
	if(now==end){
		cout<<val;
		flag=true;
		return;
	}
	for(int i=1;i<n;i++){
		if(b[i].s==now and not vis[b[i].e]){
			vis[now]=true;
			dfs(b[i].e,end,val^b[i].w);
			vis[now]=false;
		}
		if(b[i].e==now and not vis[b[i].s]){
			vis[now]=true;
			dfs(b[i].s,end,val^b[i].w);
			vis[now]=false;
		}
	}
}
signed main(){
	ios::sync_with_stdio(false);
	cin>>n;
	for(int i=1;i<=n-1;i++){
		cin>>b[i].s>>b[i].e>>b[i].w;
	}
	cin>>m;
	for(int i=1;i<=m;i++){
		int a,b;
		cin>>a>>b;
		dfs(a,b,0);
	}
	return 0;
}