Submission #589190

#	Time	Username	Problem	Language	Result	Execution time	Memory
589190		jiahng	Star Trek (CEOI20_startrek)	C++14	7 / 100	7 ms	9748 KiB

startrek

#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
#define int ll
typedef pair<int,int> pi;
typedef vector <int> vi;
typedef vector <pi> vpi;
typedef pair<pi, ll> pii;
typedef set <ll> si;
typedef long double ld;
#define f first
#define s second
#define mp make_pair
#define FOR(i,s,e) for(int i=s;i<=int(e);++i)
#define DEC(i,s,e) for(int i=s;i>=int(e);--i)
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define lbd(x, y) lower_bound(all(x), y)
#define ubd(x, y) upper_bound(all(x), y)
#define aFOR(i,x) for (auto i: x)
#define mem(x,i) memset(x,i,sizeof x)
#define fast ios_base::sync_with_stdio(false),cin.tie(0),cout.tie(0)
#define maxn 400010
#define INF (ll)(1e9+10)
#define MOD 1000000007
typedef pair <vi, int> pvi;
typedef pair <int,pi> ipi;
typedef vector <pii> vpii;
typedef pair <pi,pi> pipi;

int N,D,a,b;
vi adj[maxn];

bool win[maxn];
int firstpar[maxn], depth[maxn];

void dfs(int x, int p){
	win[x] = 0;
	aFOR(i,adj[x]) if (i != p){
		depth[i] = depth[x] + 1; dfs(i,x);
		win[x] |= !win[i];
	}
}

void dfs2(int x,int p){
	if (p == -1) firstpar[x] = x;
	else{
		firstpar[x] = firstpar[p];
		aFOR(i, adj[p]) if (depth[i] == depth[x] && i != x && !win[i]){
			firstpar[x] = x;
		}
	}
	aFOR(i,adj[x]) if (i != p) dfs2(i,x);
}
bool gwin[maxn];
int sm[maxn];

void dfs3(int x,int p){
	int n = 0;
	gwin[x] = win[x];
	aFOR(i,adj[x]) n += !win[i];
	aFOR(i,adj[x]) if (i != p){
		bool iwini = win[i];
		win[x] = (n-1 > 0);
		win[i] |= !win[x];
		
		sm[x] -= !iwini;
		sm[x] += win[x] - (n > 0);
		
		sm[i] += win[x];
		sm[i] += win[i] - iwini;
		
		dfs3(i,x);
		win[x] = (n > 0);
		win[i] = iwini;
	}
}

void dfs4(int x,int p){
	
	
	
}
int qexp(int a,int b){
	int ans = 1;
	while (b){
		//~ cout << a << ' ' << b << ' ' << ans << '\n';
		if (b & 1) (ans *= a) %= MOD;
		(a *= a) %= MOD;
		b >>= 1;
	}
	return ans;
}
int32_t main(){
    fast;
    cin >> N >> D;
    FOR(i,1,N-1){
		cin >> a >> b; adj[a].pb(b); adj[b].pb(a);
	}
	//~ cout << qexp(N, 2 * D);
	//~ return 0;
	int numnexte = 0,numnexto = 0, numwin = 0;
	
	int ans = 0;
	int nnexte1 = 0, nnexto1 = 0, nwin1 = 0;
	
	depth[1] = 0; dfs(1,-1); dfs2(1,-1); dfs3(1,-1);
	
	FOR(i,1,N){
		depth[i] = 0; dfs(i,-1); dfs2(i,-1);
		ans += win[i];
		//~ FOR(j,1,N) 
		int nnexte = 0,nnexto = 0, nwin = 0;
		FOR(j,1,N){
			if (win[j]){
				nwin++;
				if (j == 1) nwin1++;
			}else if (firstpar[j] == i){
				if (depth[j] % 2 == 0){
					nnexte++; if (j == 1) nnexte1++;
				}else{
					nnexto++; if (j == 1) nnexto1++;
				}
			
			}else if (gwin[i]){
				nwin++; if (j == 1) nwin1++;
			}
		}
		numnexte += nnexte; numnexto += nnexto; numwin += nwin;
	}
	//~ cout << nnexte1 << ' ' << nnexto1 << '\n';
	nnexte1 = nnexto1 = 0;
	depth[1] = 0;dfs(1,-1); dfs2(1,-1);
	//~ FOR(i,1,N) cout << firstpar[i] << ' ';
	//~ cout << '\n';
	FOR(i,1,N) if (firstpar[i] == 1 && !win[i]){
		if (depth[i] % 2 == 0) nnexte1++;
		else nnexto1++;
	}
	//~ cout << nnexte1 << ' ' << nnexto1 << '\n';
	if (D > 1){
		int m = numnexto - numnexte, c = numwin + numnexte;
		
		
		int r = (m * qexp((N*N)%MOD, MOD - 2)) % MOD; //mN^-2
		
		ans = (qexp(m, D - 1) * ans) % MOD;
		
		int geomseries = ((qexp(r, D - 1) - 1) * qexp(r - 1, MOD - 2)) % MOD;
		ans += (((geomseries * qexp(N, 2*(D-1)-1)) % MOD) * c) % MOD;
		(ans += MOD) %= MOD;
	}
		
	ans = (((nnexto1 - nnexte1) * ans) % MOD + (qexp(N, 2*D-1)* (nwin1 + nnexte1)) % MOD) % MOD;
	cout << (ans + MOD) % MOD;
}

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