結果

問題 No.196 典型DP (1)
コンテスト
ユーザー polylogK
提出日時 2020-04-01 05:46:35
言語 C++14
(gcc 13.3.0 + boost 1.87.0)
結果
AC  
実行時間 26 ms / 2,000 ms
コード長 4,310 bytes
コンパイル時間 1,818 ms
コンパイル使用メモリ 176,160 KB
実行使用メモリ 26,624 KB
最終ジャッジ日時 2024-06-25 23:09:50
合計ジャッジ時間 3,754 ms
ジャッジサーバーID
（参考情報） 		judge2 / judge1
このコードへのチャレンジ
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ファイルパターン 結果
sample AC * 3
other AC * 41
権限があれば一括ダウンロードができます

ソースコード

diff # 

#include <bits/stdc++.h>
using namespace std::literals::string_literals;
using i64 = std::int_fast64_t;
using std::cout;
using std::cerr;
using std::endl;
using std::cin;

template<typename T>
std::vector<T> make_v(size_t a){return std::vector<T>(a);}

template<typename T,typename... Ts>
auto make_v(size_t a,Ts... ts){
  return std::vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));
}

#ifndef INCLUDED_MODINT_HPP
#define INCLUDED_MODINT_HPP

#include <iostream>

template <std::uint_fast64_t Modulus>
class modint {
	using u32 = std::uint_fast32_t;
	using u64 = std::uint_fast64_t;
	using i64 = std::int_fast64_t;

	inline u64 apply(i64 x) { return (x < 0 ? x + Modulus : x); };

public:
	u64 a;
	static constexpr u64 mod = Modulus;

	constexpr modint(const i64& x = 0) noexcept: a(apply(x % (i64)Modulus)) {}

	constexpr modint operator+(const modint& rhs) const noexcept { return modint(*this) += rhs; }
	constexpr modint operator-(const modint& rhs) const noexcept { return modint(*this) -= rhs; }	
	constexpr modint operator*(const modint& rhs) const noexcept { return modint(*this) *= rhs; }
	constexpr modint operator/(const modint& rhs) const noexcept { return modint(*this) /= rhs; }
	constexpr modint operator^(const u64& k) const noexcept { return modint(*this) ^= k; }
	constexpr modint operator^(const modint& k) const noexcept { return modint(*this) ^= k.value(); }
	constexpr modint operator-() const noexcept { return modint(Modulus - a); }
	constexpr modint operator++() noexcept { return (*this) = modint(*this) + 1; }
	constexpr modint operator--() noexcept { return (*this) = modint(*this) - 1; }
	const bool operator==(const modint& rhs) const noexcept { return a == rhs.a; };
	const bool operator!=(const modint& rhs) const noexcept { return a != rhs.a; };
	const bool operator<=(const modint& rhs) const noexcept { return a <= rhs.a; };
	const bool operator>=(const modint& rhs) const noexcept { return a >= rhs.a; };
	const bool operator<(const modint& rhs) const noexcept { return a < rhs.a; };
	const bool operator>(const modint& rhs) const noexcept { return a > rhs.a; };
	constexpr modint& operator+=(const modint& rhs) noexcept {
		a += rhs.a;
		if (a >= Modulus) a -= Modulus;
		return *this;
	}
	constexpr modint& operator-=(const modint& rhs) noexcept {
		if (a < rhs.a) a += Modulus;
		a -= rhs.a;
		return *this;
	}
	constexpr modint& operator*=(const modint& rhs) noexcept {
		a = a * rhs.a % Modulus;
		return *this;
	}
	constexpr modint& operator/=(modint rhs) noexcept {
		u64 exp = Modulus - 2;
		while (exp) {
			if (exp % 2) (*this) *= rhs;
			
			rhs *= rhs;
			exp /= 2;
		}
		return *this;
	}
	constexpr modint& operator^=(u64 k) noexcept {
		auto b = modint(1);
		while(k) {
			if(k & 1) b = b * (*this);
			(*this) *= (*this);
			k >>= 1;
		}
		return (*this) = b;
	}
	constexpr modint& operator=(const modint& rhs) noexcept {
		a = rhs.a;
		return (*this);
	}

	constexpr u64& value() noexcept { return a; }
	constexpr const u64& value() const noexcept { return a; }
	explicit operator bool() const { return a; }
	explicit operator u32() const { return a; }

	const modint inverse() const {
		return modint(1) / *this;
	}
	const modint pow(i64 k) const {
		return modint(*this) ^ k;
	}

	friend std::ostream& operator<<(std::ostream& os, const modint& p) {
		return os << p.a;
	}
	friend std::istream& operator>>(std::istream& is, modint& p) {
		u64 t;
		is >> t;
		p = modint(t);
		return is;
	}
};

#endif

using mint = modint<(int)(1e9 + 7)>;

int main() {
	int n, k; scanf("%d%d", &n, &k);
	std::vector<int> a(n - 1), b(n - 1);
	std::vector<std::vector<int>> g(n);
	for(int i = 0; i < n - 1; i++) {
		scanf("%d%d", &a[i], &b[i]);

		g[a[i]].push_back(i);
		g[b[i]].push_back(i);
	}

	std::vector<std::vector<mint>> vec(n);
	auto solve = [&](auto&& solve, int v, int par) -> void {
		int now = 1;
		vec[v].resize(now); vec[v][0] = 1;
		for(int id: g[v]) {
			int to = a[id] ^ b[id] ^ v;
			if(to == par) continue;
			solve(solve, to, v);

			std::vector<mint> nxt(now += (int)vec[to].size() - 1);
			for(int i = 0; i < vec[v].size(); i++)
				for(int j = 0; j < vec[to].size(); j++)
					nxt[i + j] += vec[v][i] * vec[to][j];
			vec[v].swap(nxt);
		}
		vec[v].push_back(1);
	};
	solve(solve, 0, -1);

	printf("%lld\n", vec[0][k].value());
	return 0;
}
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