結果

問題 No.1124 Earthquake Safety
コンテスト
ユーザー QCFium
提出日時 2020-07-03 14:39:30
言語 C++14
(gcc 13.3.0 + boost 1.87.0)
結果
AC  
実行時間 346 ms / 3,000 ms
コード長 3,071 bytes
コンパイル時間 1,830 ms
コンパイル使用メモリ 177,056 KB
実行使用メモリ 67,840 KB
最終ジャッジ日時 2024-09-16 17:08:07
合計ジャッジ時間 17,760 ms
ジャッジサーバーID
（参考情報） 		judge4 / judge5
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ファイルパターン 結果
other AC * 58
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ソースコード

diff # 

#include <bits/stdc++.h>

int ri() {
	int n;
	scanf("%d", &n);
	return n;
}


template<int mod>
struct ModInt{
	int x;
	ModInt () : x(0) {}
	ModInt (int64_t x) : x(x >= 0 ? x % mod : (mod - -x % mod) % mod) {}
	ModInt &operator += (const ModInt &p){
		if ((x += p.x) >= mod) x -= mod;
		return *this;
	}
	ModInt &operator -= (const ModInt &p) {
		if ((x += mod - p.x) >= mod) x -= mod;
		return *this;
	}
	ModInt &operator *= (const ModInt &p) {
		x = (int64_t) x * p.x % mod;
		return *this;
	}
	ModInt &operator /= (const ModInt &p) {
		*this *= p.inverse();
		return *this;
	}
	ModInt &operator ^= (int64_t p) {
		ModInt res = 1;
		for (; p; p >>= 1) {
			if (p & 1) res *= *this;
			*this *= *this;
		}
		return *this = res;
	}
	ModInt operator - () const { return ModInt(-x); }
	ModInt operator + (const ModInt &p) const { return ModInt(*this) += p; }
	ModInt operator - (const ModInt &p) const { return ModInt(*this) -= p; }
	ModInt operator * (const ModInt &p) const { return ModInt(*this) *= p; }
	ModInt operator / (const ModInt &p) const { return ModInt(*this) /= p; }
	ModInt operator ^ (int64_t p) const { return ModInt(*this) ^= p; }
	bool operator == (const ModInt &p) const { return x == p.x; }
	bool operator != (const ModInt &p) const { return x != p.x; }
	explicit operator int() const { return x; }
	ModInt &operator = (const int p) { x = p; return *this;}
	ModInt inverse() const {
		int a = x, b = mod, u = 1, v = 0, t;
		while (b > 0) {
			t = a / b;
			a -= t * b;
			std::swap(a, b);
			u -= t * v;
			std::swap(u, v);
		}
		return ModInt(u);
	}
	friend std::ostream & operator << (std::ostream &stream, const ModInt<mod> &p) {
		return stream << p.x;
	}
	friend std::istream & operator >> (std::istream &stream, ModInt<mod> &a) {
		int64_t x;
		stream >> x;
		a = ModInt<mod>(x);
		return stream;
	}
};

#define MOD 1000000007
typedef ModInt<MOD> mint;


std::vector<std::vector<int> > hen;

std::vector<mint> subtree_dsum;
void dfs0(int i, int prev) {
	subtree_dsum[i] = mint(1) / 2;
	for (auto j : hen[i]) if (j != prev) {
		dfs0(j, i);
		subtree_dsum[i] += subtree_dsum[j] / 2;
	}
}

mint res = 0;
void dfs1(int i, int prev, mint prev_dsum) {
	std::vector<mint> all;
	if (prev != -1) all.push_back(prev_dsum);
	for (auto j : hen[i]) if (j != prev) all.push_back(subtree_dsum[j]);
	
	mint sum = std::accumulate(all.begin(), all.end(), (mint) 0);
	mint sum2 = std::accumulate(all.begin(), all.end(), (mint) 0, [] (mint a, mint b) { return a + b * b; });
	mint sum3 = std::accumulate(all.begin(), all.end(), (mint) 0, [] (mint a, mint b) { return a + b * b * b; });
	
	res += sum * sum * sum - sum2 * sum * 3 + sum3 * 2;
	res += (sum * sum - sum2) * 3;
	res += sum * 3 + 1;
	
	for (auto j : hen[i]) if (j != prev) dfs1(j, i, (sum - subtree_dsum[j] + 1) / 2);
}

int main() {
	int n = ri();
	hen.resize(n);
	for (int i = 1; i < n; i++) {
		int a = ri() - 1;
		int b = ri() - 1;
		hen[a].push_back(b);
		hen[b].push_back(a);
	}
	subtree_dsum.resize(n);
	dfs0(0, -1);
	dfs1(0, -1, 0);
	res *= mint(2) ^ (n - 1);
	printf("%d\n", res.x);
	return 0;
}
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