Codeforces Round #665 (Div. 2) D. Maximum Distributed Tree

考点：图论，数论。

#include 
#include 
#include 
#include 
using namespace std;
const int maxn = 100010;
const long long mod = 1e9+7;
long long p[maxn];
vector<long long> v[maxn];
long long vis[maxn] = {0};
long long sum[maxn] = {0};
long long b[maxn];

void dfs(long long x){
	sum[x]++;
	for(long long i = 0;i<v[x].size() ;i++){
		long long y = v[x][i];
		if(vis[y]) continue;
		vis[y] = 1;
		dfs(y);
		sum[x] += sum[y];
	}
}

int main(){
	long long t;
	cin >> t;
	while(t--){
		long long n;
		cin >> n;
		memset(vis,0,sizeof(long long)*(n+10));
		memset(sum,0,sizeof(long long)*(n+10));
		long long s,t;
		for(long long i = 0;i<n-1;i++){
			cin >> s >> t;
			v[s].push_back(t);
			v[t].push_back(s);
		}
		vis[1] = 1;
		dfs(1);
		long long tt = 0;
		for(long long i = 0;i<n;i++){
			long long x = i+1;;
			if(sum[x] == n) continue;
			b[tt++] = (n-sum[x])*sum[x]%mod;
		} 
		sort(b,b+n-1);
		long long m;
		cin >> m;
		long long sum = 0;
		for(long long i = 0;i<m;i++){
			cin >> p[i];
		}
		sort(p,p+m);
		if(m<n-1){
			long long u = n-1-m;
			for(long long i = m-1;i >= 0;i--){
				p[i+u] = p[i];
			}
			for(long long i = 0;i<u;i++){
				p[i] = 1;
			}
		}
		else {
			long long u = m-n+1;
			for(long long i = m-1;i >= m-u;i--){
				p[m-u-1] = (p[m-u-1]*p[i])%mod;
			}
		}
		long long ans = 0;
		for(long long i = 0;i<n-1;i++){
			ans = (ans+b[i]*p[i]%mod)%mod;
		}
		cout << (ans%mod+mod)%mod << endl;
		for(long long i = 1;i <= n;i++){
			v[i].clear() ;
		}
	}
	return 0;
}