Submission #999053

#	Time	Username	Problem	Language	Result	Execution time	Memory
999053		vjudge1	Sumtree (INOI20_sumtree)	C++17	30 / 100	3065 ms	72276 KiB

Main

#include <bits/stdc++.h>

using namespace std;

#define int long long

const int MXN = 1e6 + 5;
const int mod = 1e9 + 7;

int n, r;
vector<int> adj[MXN];
int f[MXN], tag[MXN], sum[MXN], x[MXN], delsz[MXN], sz[MXN], del[MXN];

int pw(int a, int b, int c)
{
	a %= c;
	int res = 1;
	while (b)
	{
		if (b & 1) res = (res * a) % mod;
		a = (a * a) % mod;
		b >>= 1;
	}
	return res;
}

int nck(int n, int k)
{
	if (min(n, k) < 0 || k > n) return 0;
	return (f[n] * pw((f[n - k] * f[k]) % mod, mod - 2, mod)) % mod;
}

void dfs(int a, int p)
{
	sz[a] = 1, delsz[a] = 0;
	sum[a] = 0;
	for (int &v : adj[a])
	{
		if (v == p) continue;
		dfs(v, a);
		sum[a] += sum[v];
		sz[a] += sz[v];
		delsz[a] += delsz[v];
 	}
	x[a] = sum[a];
	if (tag[a] != -1) 
	{
		sum[a] = tag[a];
		del[a] = delsz[a];
		delsz[a] = sz[a];
	}
}

int calc()
{
	int res = 1;
	for (int i = 1; i <= n; i++)
	{
		if (tag[i] == -1) continue;
		if (x[i] > tag[i]) return 0;
		res = (res * nck(sz[i] - del[i] - 1 + tag[i] - x[i], tag[i] - x[i])) % mod;
	}
	return res;
}

signed main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	f[0] = 1;
	for (int i = 1; i < MXN; i++) 
	{
		f[i] = (f[i - 1] * i) % mod;
		tag[i] = -1;
	}
	cin >> n >> r;
	tag[1] = r;
	for (int i = 1; i < n; i++)
	{
		int u, v;
		cin >> u >> v;
		adj[u].push_back(v);
		adj[v].push_back(u);
	}
	int q;
	cin >> q;
	dfs(1, 1);
	cout << calc() << '\n';
	while (q--)
	{
		int t;
		cin >> t;
		if (t == 1)
		{
			int u, v;
			cin >> u >> v;
			tag[u] = v;
		}
		else
		{
			int u;
			cin >> u;
			tag[u] = -1;
		}
		dfs(1, 1);
		cout << calc() << '\n';
	}
}

• Subtask 1: 10 / 10
• Subtask 2: 20 / 20
• Subtask 3: 0 / 20
• Subtask 4: 0 / 20
• Subtask 5: 0 / 30