hdu 2586 How far away ？（LCA）

/********************************************
**题意是给你一颗树，求树上任意两节点 u ，v 的距离
**所求 u，v 的距离可以用最近公共祖先求得
**设 x 为 u，v 的最近公共祖先，dis[i]为第 i 个结点到树根的距离
**则所求为 dis[u]+dis[v]-2*dis[x];
********************************************/
#pragma comment(linker, "/STACK:1024000000,1024000000")
#include <iostream>
#include <vector>
#define N 40010
using namespace std;

vector<int>to[N], w[N], query[N], id[N];
int father[N], dis[N];
int ans[205];
bool vis[N];

void init(int n, int m){
	for (int i = 0; i <= n; i++){
		father[i] = 0;
		vis[i] = false;
		dis[i] = 0;
		to[i].clear();
		w[i].clear();
		query[i].clear();
		id[i].clear();
	}
}

void add(int u, int v, int c){
	to[u].push_back(v);
	w[u].push_back(c);
}

int find_set(int x){
	if (x == father[x])return father[x];
	return father[x] = find_set(father[x]);
}

void union_set(int x, int y){
	x = find_set(x);
	y = find_set(y);
	father[y] = x;
}

void dfs(int u, int d){

	father[u] = u;
	vis[u] = true;
	dis[u] = d;

	for (int i = 0; i < to[u].size(); i++){
		int v = to[u][i];
		if (vis[v] == false){
			dfs(v, d + w[u][i]);
			union_set(u, v);
		}
	}

	for (int i = 0; i < query[u].size(); i++){
		int v = query[u][i];
		if (vis[v] == true){
			ans[id[u][i]] = dis[v] + dis[u] - 2 * dis[find_set(v)];
		}
	}

}

int main(){
	int t, n, m;
	cin >> t;
	while (t--){
		cin >> n >> m;
		init(n, m);
		int u, v, c;
		for (int i = 1; i < n; i++){
			cin >> u >> v >> c;
			add(u, v, c);
			add(v, u, c);
		}

		for (int i = 1; i <= m; i++){
			cin >> u >> v;
			query[u].push_back(v);
			query[v].push_back(u);
			id[u].push_back(i);
			id[v].push_back(i);
		}

		dfs(1, 0);

		for (int i = 1; i <= m; i++){
			cout << ans[i] << endl;
		}
	}
	return 0;
}