結果

問題 No.1103 Directed Length Sum
ユーザー m_tsubasa
提出日時 2020-07-22 14:38:20
言語 C++17
(gcc 13.3.0 + boost 1.87.0)
結果
AC  
実行時間 1,290 ms / 3,000 ms
コード長 2,639 bytes
コンパイル時間 2,571 ms
コンパイル使用メモリ 200,016 KB
最終ジャッジ日時 2025-01-12 01:57:15
ジャッジサーバーID
（参考情報） 		judge3 / judge1
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ファイルパターン 結果
sample AC * 2
other AC * 22
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;

template <int mod = (int)(1e9 + 7)>
struct ModInt {
  int x;
  constexpr ModInt() : x(0) {}
  constexpr ModInt(int64_t y)
      : x(y >= 0 ? y % mod : (mod - (-y) % mod) % mod) {}
  constexpr ModInt &operator+=(const ModInt &p) noexcept {
    if ((x += p.x) >= mod) x -= mod;
    return *this;
  }
  constexpr ModInt &operator-=(const ModInt &p) noexcept {
    if ((x += mod - p.x) >= mod) x -= mod;
    return *this;
  }
  constexpr ModInt &operator*=(const ModInt &p) noexcept {
    x = (int)(1LL * x * p.x % mod);
    return *this;
  }
  constexpr ModInt &operator/=(const ModInt &p) noexcept {
    *this *= p.inverse();
    return *this;
  }
  constexpr ModInt operator-() const { return ModInt(-x); }
  constexpr ModInt operator+(const ModInt &p) const noexcept {
    return ModInt(*this) += p;
  }
  constexpr ModInt operator-(const ModInt &p) const noexcept {
    return ModInt(*this) -= p;
  }
  constexpr ModInt operator*(const ModInt &p) const noexcept {
    return ModInt(*this) *= p;
  }
  constexpr ModInt operator/(const ModInt &p) const noexcept {
    return ModInt(*this) /= p;
  }
  constexpr bool operator==(const ModInt &p) const noexcept { return x == p.x; }
  constexpr bool operator!=(const ModInt &p) const noexcept { return x != p.x; }
  constexpr ModInt inverse() const noexcept {
    int a = x, b = mod, u = 1, v = 0, t = 0;
    while (b > 0) {
      t = a / b;
      swap(a -= t * b, b);
      swap(u -= t * v, v);
    }
    return ModInt(u);
  }
  constexpr ModInt pow(int64_t n) const {
    ModInt res(1), mul(x);
    while (n) {
      if (n & 1) res *= mul;
      mul *= mul;
      n >>= 1;
    }
    return res;
  }
  friend constexpr ostream &operator<<(ostream &os, const ModInt &p) noexcept {
    return os << p.x;
  }
  friend constexpr istream &operator>>(istream &is, ModInt &a) noexcept {
    int64_t t = 0;
    is >> t;
    a = ModInt<mod>(t);
    return (is);
  }
  constexpr int get_mod() { return mod; }
};

int n, root = -1;
vector<int> cnt, dp;
vector<vector<int>> g;

ModInt<> solve(int now, int par, int dist);

int main() {
  cin >> n;
  g.resize(n);
  dp.assign(n, 1);
  cnt.assign(n, 0);
  for (int i = 1; i < n; ++i) {
    int a, b;
    cin >> a >> b;
    g[--a].push_back(--b);
    ++cnt[b];
  }
  for (int i = 0; i < n; ++i)
    if (cnt[i] == 0) root = i;
  cout << solve(root, -1, 0) << endl;
  return 0;
}

ModInt<> solve(int now, int par, int dist) {
  ModInt<> res = 0;
  for (auto to : g[now])
    if (to != par) {
      res += solve(to, now, dist + 1);
      dp[now] += dp[to];
    }
  res += ModInt<>(dp[now]) * dist;
  return res;
}
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