求树上两点之间路径上最小边权

#include<bits/stdc++.h>
using namespace std;
#define ll long long
const int N = 5e5+5;
int n, q, root;
int head[N], nxt[N << 1], to[N << 1], cccnnnttt, val[N << 1];
int fa[N][20], dep[N], minw[N][20];
void add(int u, int v, int w){
	to[++cccnnnttt] = v;
	val[cccnnnttt] = w;
	nxt[cccnnnttt] = head[u];
	head[u] = cccnnnttt;
}
void dfs(int u, int f){
	fa[u][0] = f;
	for (int i = 1;i <= 18;i++){
		fa[u][i] = fa[fa[u][i - 1]][i - 1];
		minw[u][i] = min(minw[u][i - 1], minw[fa[u][i - 1]][i - 1]);
	}
	for (int i = head[u];i;i = nxt[i]){
		int v = to[i], w = val[i];
		if (v == f) continue;
		dep[v] = dep[u] + 1;
		minw[v][0] = w;
		dfs(v, u);
	}
}
int LCA(int u, int v){
	if (dep[u] < dep[v]) swap(u, v);
	int res = INT_MAX;
	for (int i = 18;i >= 0;i--){
		if (dep[fa[u][i]] >= dep[v]){
			u = fa[u][i];
			res = min(res, minw[u][i]);
		}
	}
	if (u == v) return res;
	for (int i = 18;i >= 0;i--){
		if (fa[u][i] != fa[v][i]){
			u = fa[u][i];
			v = fa[v][i];
			res = min(res, min(minw[u][i], minw[v][i]));
		}
	}
	res = min(res, min(minw[u][0], minw[v][0]));
	return res;
}
int main(){
	//ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
	//memset(minw, 0x3f3f3f3f, sizeof minw);
	cin >> n >> q ;
	for (int i = 1;i < n;i++){
		int u, v, w;
		cin >> u >> v >> w;
		add(u, v, w);
		add(v, u, w);
	}
	dep[1] = 1;
	dfs(1, 0);
	while (q--){
		int x, y;
		cin >> x >> y;
		cout << LCA(x, y) << '\n';
	}
	return 0;
}