제출 #390145

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
390145		talant117408	Star Trek (CEOI20_startrek)	C++17	45 / 100	112 ms	16684 KiB

startrek

/*
    Code written by Talant I.D.
*/
#include <bits/stdc++.h>
 
using namespace std;
 
typedef long long ll;
typedef pair <int, int> pii;
typedef pair <ll, ll> pll;
 
#define precision(n) fixed << setprecision(n)
#define pb push_back
#define ub upper_bound
#define lb lower_bound
#define mp make_pair
#define eps (double)1e-9
#define PI 2*acos(0.0)
#define endl "\n"
#define sz(v) int((v).size())
#define all(v) v.begin(),v.end()
#define rall(v) v.rbegin(),v.rend()
#define do_not_disturb ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define OK cout << "OK" << endl;
 
const int mod = 1e9+7;
 
ll mode(ll a) {
    a %= mod;
    if (a < 0) a += mod;
    return a;
}
 
ll subt(ll a, ll b) {
    return mode(mode(a)-mode(b));
}
 
ll add(ll a, ll b) {
    return mode(mode(a)+mode(b));
}
 
ll mult(ll a, ll b) {
    return mode(mode(a)*mode(b));
}
 
ll binpow(ll a, ll b) {
    ll res = 1;
    while (b) {
        if (b&1) res = mult(res, a);
        a = mult(a, a);
        b >>= 1;
    }
    return res;
}

const int N = 1e5+7;
int state[N], l, w, state_as_root[N];
int losing_children[N], critical[N], depth[N], par[N];
ll dp[N];
vector <int> graph[N];

bool dfs(int v, int p) {
	par[v] = p;
	depth[v] = depth[p]+1;
	int cnt = 0, children = 0;
	for (auto to : graph[v]) {
		if (to == p) continue;
		children++;
		dfs(to, v);
		cnt += (state[to] ? 1 : 0);
		if (state[to]) losing_children[v]++;
	}
	if (children == 0) state[v] = 1;
	else if (cnt) state[v] = 0;
	else state[v] = 1;
	return state[v];
}

void dfs2(int v, int p, int origin, int cnt = 0) {
	if (cnt == depth[v] && state[v]) critical[origin]++;
	if (state[v]) {
		for (auto to : graph[v]) {
			if (to == p) continue;
			dfs2(to, v, origin, cnt+1);
		}
	}
	else {
		for (auto to : graph[v]) {
			if (to == p) continue;
			if (state[to]) {
				dfs2(to, v, origin, (losing_children[v] == 1 ? cnt+1 : 0));
			}
		}
	}
}

void dfs3(int v, int p) {
	state_as_root[v] = state[v];
	if (state[v]) l++;
	else w++;
	for (auto to : graph[v]) {
		if (to == p) continue;
		if (state[v] == false && state[to] == true) {
			if (losing_children[v] == 1 && (state_as_root[par[v]] == false)) {
				losing_children[v]--;
				losing_children[to]++;
				state[v] = 1;
				state[to] = 0;
				dfs3(to, v);
				losing_children[v]++;
				losing_children[to]--;
				state[v] = 0;
				state[to] = 1;
			}
			else {
				dfs3(to, v);
			}
		}
		else {
			dfs3(to, v);
		}
	}
}

int main() {
	do_not_disturb
	
	int n;
	ll d;
	cin >> n >> d;
	for (int i = 0; i < n-1; i++) {
		int x, y;
		cin >> x >> y;
		graph[x].pb(y);
		graph[y].pb(x);
	}
	
	if (n == 2) {
		cout << binpow(2, d*2);
	}
	else if (d == 1) {
		depth[1] = -1;
		dfs(1, 1);
		dfs2(1, 1, 1);
		dfs3(1, 1);
		if (state_as_root[1]) cout << mult(critical[1], l);
		else cout << add(mult(n, w), mult(subt(n, critical[1]), l));
	}
	else if (d <= 1e5) {
		depth[1] = -1;
		dfs(1, 1);
		dfs3(1, 1);
		for (int i = 1; i <= n; i++) {
			depth[i] = -1;
			for (int j = 1; j <= n; j++) losing_children[j] = 0;
			dfs(i, i);
			dfs2(i, i, i);
		}
		dp[0] = l;
		ll E = 0;
		for (int i = 1; i <= n; i++) {
			if (state[i]) {
				E = subt(E, critical[i]);
			}
			else {
				E = add(E, critical[i]);
			}
		}
		for (int i = 1; i <= d; i++) {
			dp[i] = add(mult(l, binpow(n, 2*(d-i))), mult(E, dp[i-1]));
		}
		cout << (state[1] ? mult(dp[d-1], critical[1]) : subt(binpow(n, 2*d), mult(dp[d-1], critical[1]))) << endl;
	}
	
    return 0;
}

• Subtask 1: 0 / 0
• Subtask 2: 7 / 7
• Subtask 3: 8 / 8
• Subtask 4: 15 / 15
• Subtask 5: 15 / 15
• Subtask 6: 0 / 20
• Subtask 7: 0 / 20
• Subtask 8: 0 / 15