555，爆6分，求助

#include <bits/stdc++.h>
using namespace std;
const int N = 50005;
int n, k, d[N], f[N][25], sum[N], ans;
vector <int> E[N];
void init(int x, int fa) {
	for (int i = 0; i < E[x].size(); ++i) {
		if (E[x][i] == fa) continue;
		d[E[x][i]] = d[x] + 1;
		f[E[x][i]][0] = x;
		init(E[x][i], x);
	}
}
int query(int u, int v) {
	if (d[u] > d[v]) swap(u, v);
	int k = d[v] - d[u];
	for (int i = 20; ~i; --i) {
		if (k >= (1 << i)) k -= (1 << i), v = f[v][i];
		if (k == 0) break;
	}
	if (u == v) return u;
	for (int i = 20; ~i; --i)
		if (f[u][i] != f[v][i]) u = f[u][i], v = f[v][i];
	return f[u][0];
}
void dfs(int x, int fa) {
	for (int i = 0; i < E[x].size(); ++i) {
		if (E[x][i] == fa) continue;
		dfs(E[x][i], x);
		sum[x] += sum[E[x][i]];
	}
//	cout << x << ' ' << sum[x] << endl;
	ans = max(ans, sum[x]);
}
int main() {
	cin >> n >> k;
	for (int i = 1; i < n; ++i) {
		int u, v;
		cin >> u >> v;
		E[u].push_back(v), E[v].push_back(u);
	}
	d[1] = 1, f[1][0] = 1;
	init(1, -1);
	for (int j = 1; j <= 20; ++j)
		for (int i = 1; i <= n; ++i)
			f[i][j] = f[f[i - 1][j]][j - 1];
	while (k--) {
		int S, T;
		cin >> S >> T;
		int p = query(S, T);
		++sum[S], ++sum[T], --sum[p], --sum[f[p][0]];
	}
	dfs(1, -1);
//	printf("%d", sum[1]);
	printf("%d", ans);
	return 0;	
}