P1967 货车运输 -60分

打了一个最大生成树+dfs，60分成功tle

#include <bits/stdc++.h>
using namespace std;
const int maxn = 10005;
const int maxm = 50005;
int n, m, cnt = 0;
struct edge
{
	int from, to, value;
	bool operator < (const edge b) const {
		return this->value > b.value;
	}
}es[maxm];
vector<edge> G[maxn];
struct car
{
	int from, to;
}cs[30001];
int q;
void read() {
	cin >> n >> m;
	for(int i = 1; i <= m; i++) {
		int x, y, z;
		cin >> x >> y >> z;
		es[cnt].from = x;
		es[cnt].to = y;
		es[cnt].value = z;
		cnt++; 
	}
	cin >> q;
	for(int i = 1; i <= q; i++) cin >> cs[i].from >> cs[i].to;
}
int fa[maxn];
int find(int x) {
	return x == fa[x] ? x : fa[x] = find(fa[x]);
}
void kruskal() {
	sort(es, es+cnt);
	for(int i = 1; i <= n; i++) fa[i] = i;
	for(int i = 0; i < cnt; i++) {
		int x = es[i].from; int y = es[i].to;
		int fx = find(x); int fy = find(y);
		if(fx == fy) {
			es[i].value = -1;
			continue;
		}
		else fa[fx] = fy;
	}
}
void build_tree() {
	sort(es, es+cnt);
	for(int i = 0; i < cnt; i++) {
		if(es[i].value != -1) {
			int x = es[i].from;
			int y = es[i].to;
			G[x].push_back({x, y, es[i].value});
			G[y].push_back({y, x, es[i].value});
		}
		else break;
	}
}
int mini = 0x3f3f3f;
int vis[maxn];
void dfs(int from, int to, int m) {
	vis[from] = 1;
	if(from == to) {mini = m; return;}
	vector<edge>::iterator it;
	for(it = G[from].begin(); it != G[from].end(); it++) {
		edge &e = *it;
		if(!vis[e.to]) {
			dfs(e.to, to, min(m, e.value));
		}
	}
}
void solve() {
	for(int i = 1; i <= q; i++) {
		int x = cs[i].from;
		int y = cs[i].to;
		mini = 0x3f3f3f;
		memset(vis, 0, sizeof(vis));
		dfs(x, y, 0x3f3f3f);
		if(mini == 0x3f3f3f) cout << -1;
		else cout << mini;
		cout << endl;
	}
}
int main() {
//	freopen("input.in", "r", stdin);
	read();
	kruskal();
	build_tree();
	solve();
	return 0;
}