結果

問題 No.1333 Squared Sum
ユーザー satashun
提出日時 2021-01-08 22:00:40
言語 C++17
(gcc 13.3.0 + boost 1.87.0)
結果
AC  
実行時間 362 ms / 2,000 ms
コード長 4,196 bytes
コンパイル時間 2,107 ms
コンパイル使用メモリ 199,916 KB
最終ジャッジ日時 2025-01-17 11:59:25
ジャッジサーバーID
（参考情報） 		judge2 / judge2
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ファイルパターン 結果
other AC * 44
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ソースコード

diff #
プレゼンテーションモードにする

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
template <class T>
using V = vector<T>;
template <class T>
using VV = V<V<T>>;
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define fi first
#define se second
#define rep(i, n) rep2(i, 0, n)
#define rep2(i, m, n) for (int i = m; i < (n); i++)
#define per(i, b) per2(i, 0, b)
#define per2(i, a, b) for (int i = int(b) - 1; i >= int(a); i--)
#define ALL(c) (c).begin(), (c).end()
#define SZ(x) ((int)(x).size())
constexpr ll TEN(int n) { return (n == 0) ? 1 : 10 * TEN(n - 1); }
template <class T, class U>
void chmin(T& t, const U& u) {
    if (t > u) t = u;
}
template <class T, class U>
void chmax(T& t, const U& u) {
    if (t < u) t = u;
}
template <class T, class U>
ostream& operator<<(ostream& os, const pair<T, U>& p) {
    os << "(" << p.first << "," << p.second << ")";
    return os;
}
template <class T>
ostream& operator<<(ostream& os, const vector<T>& v) {
    os << "{";
    rep(i, v.size()) {
        if (i) os << ",";
        os << v[i];
    }
    os << "}";
    return os;
}
#ifdef LOCAL
void debug_out() { cerr << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
    cerr << " " << H;
    debug_out(T...);
}
#define debug(...) \
    cerr << __LINE__ << " [" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#define dump(x) cerr << __LINE__ << " " << #x << " = " << (x) << endl
#else
#define debug(...) (void(0))
#define dump(x) (void(0))
#endif
template <unsigned int MOD>
struct ModInt {
    using uint = unsigned int;
    using ull = unsigned long long;
    using M = ModInt;
    uint v;
    ModInt(ll _v = 0) { set_norm(_v % MOD + MOD); }
    M& set_norm(uint _v) {  //[0, MOD * 2)->[0, MOD)
        v = (_v < MOD) ? _v : _v - MOD;
        return *this;
    }
    explicit operator bool() const { return v != 0; }
    M operator+(const M& a) const { return M().set_norm(v + a.v); }
    M operator-(const M& a) const { return M().set_norm(v + MOD - a.v); }
    M operator*(const M& a) const { return M().set_norm(ull(v) * a.v % MOD); }
    M operator/(const M& a) const { return *this * a.inv(); }
    M& operator+=(const M& a) { return *this = *this + a; }
    M& operator-=(const M& a) { return *this = *this - a; }
    M& operator*=(const M& a) { return *this = *this * a; }
    M& operator/=(const M& a) { return *this = *this / a; }
    M operator-() const { return M() - *this; }
    M& operator++(int) { return *this = *this + 1; }
    M& operator--(int) { return *this = *this - 1; }
    M pow(ll n) const {
        if (n < 0) return inv().pow(-n);
        M x = *this, res = 1;
        while (n) {
            if (n & 1) res *= x;
            x *= x;
            n >>= 1;
        }
        return res;
    }
    M inv() const {
        ll a = v, b = MOD, p = 1, q = 0, t;
        while (b != 0) {
            t = a / b;
            swap(a -= t * b, b);
            swap(p -= t * q, q);
        }
        return M(p);
    }
    bool operator==(const M& a) const { return v == a.v; }
    bool operator!=(const M& a) const { return v != a.v; }
    friend ostream& operator<<(ostream& os, const M& a) { return os << a.v; }
    static uint get_mod() { return MOD; }
};
using Mint = ModInt<1000000007>;
int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int N;
    cin >> N;
    VV<pii> g(N);
    rep(i, N - 1) {
        int a, b, w;
        cin >> a >> b >> w;
        --a, --b;
        g[a].eb(b, w);
        g[b].eb(a, w);
    }
    Mint ans;
    V<Mint> sum0(N), sum1(N), sum2(N);
    auto dfs = [&](auto&& f, int v, int p) -> void {
        sum0[v] = 1;
        for (auto& [to, w] : g[v]) {
            if (to != p) {
                f(f, to, v);
                sum2[to] += sum0[to] * w * w + sum1[to] * 2 * w;
                sum1[to] += sum0[to] * w;
                ans += sum2[v] * sum0[to] + sum2[to] * sum0[v] +
                       sum1[v] * sum1[to] * 2;
                sum2[v] += sum2[to];
                sum1[v] += sum1[to];
                sum0[v] += sum0[to];
            }
        }
    };
    dfs(dfs, 0, -1);
    cout << ans << endl;
    return 0;
}
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