結果

問題 No.1011 Infinite Stairs
ユーザー oevl
提出日時 2020-04-19 11:09:37
言語 C++17
(gcc 13.3.0 + boost 1.87.0)
結果
AC  
実行時間 1,560 ms / 2,000 ms
コード長 3,808 bytes
コンパイル時間 2,823 ms
コンパイル使用メモリ 197,432 KB
最終ジャッジ日時 2025-01-09 21:25:00
ジャッジサーバーID
（参考情報） 		judge1 / judge3
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ファイルパターン 結果
sample AC * 3
other AC * 24
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<int64_t MOD> class ModInt {
public:
    int64_t x;
    constexpr ModInt() : x(0) {}
    constexpr ModInt(int64_t v) : x((v % MOD + MOD) % MOD) {}
    constexpr ModInt operator - () const noexcept { return x ? MOD - x : 0;}
    constexpr ModInt operator + (const ModInt a) const noexcept { return ModInt(*this) += a;}
    constexpr ModInt operator - (const ModInt a) const noexcept { return ModInt(*this) -= a;}
    constexpr ModInt operator * (const ModInt a) const noexcept { return ModInt(*this) *= a;}
    constexpr ModInt operator / (const ModInt a) const noexcept { return ModInt(*this) /= a;}
    constexpr ModInt operator / (const int64_t a) const noexcept { return ModInt(*this) /= a;}
    constexpr ModInt operator += (const ModInt a) noexcept {
        x += a.x;
        if (x >= MOD) x -= MOD;
        return *this;
    }
    constexpr ModInt operator += (const int64_t a) noexcept {
        auto hs = ModInt<MOD>(a);
        (*this) += hs;
        return *this;
    }
    constexpr ModInt operator -= (const ModInt a) noexcept {
        if (x < a.x) x += MOD;
        x -= a.x;
        return *this;
    }
    constexpr ModInt operator -= (const int64_t a) noexcept {
        auto hs = ModInt<MOD>(a);
        (*this) -= hs;
        return *this;
    }
    constexpr ModInt operator *= (const ModInt a) noexcept {
        x = x * a.x % MOD;
        return *this;
    }
    constexpr ModInt operator *= (const int64_t a) noexcept {
        auto hs = ModInt<MOD>(a);
        (*this) *= hs;
        return *this;
    }
    constexpr ModInt &operator /= (ModInt a) noexcept {
        int64_t exp = MOD - 2;
        while (exp > 0) {
            if (exp & 1ul) *this *= a;
            a *= a;
            exp >>= 1ul;
        }
        return *this;
    }
    constexpr ModInt &operator /= (int64_t a) noexcept {
        auto hs = ModInt<MOD>(a);
        (*this) /= hs;
        return *this;
    }
    constexpr ModInt &operator ++ () noexcept {
        if (++x >= MOD) x -= MOD;
        return *this;
    }
    constexpr ModInt &operator -- () noexcept {
        if (x-- == 0) x += MOD;
        return *this;
    }
    constexpr bool operator < (const ModInt a) const noexcept { return x < a.x;}
    constexpr bool operator == (const ModInt a) const noexcept { return this->x == a.x;}
    constexpr bool operator != (const ModInt a) const noexcept { return !(*this == a);}
    friend istream &operator >> (istream &in, ModInt &m) {
        in >> m.x;
        if (m.x < 0) m.x += MOD;
        m.x %= MOD;
        return in;
    }
    friend ostream &operator << (ostream &out, const ModInt &p) { return out << p.x;}
    constexpr ModInt pow(int64_t p) const {
        ModInt ret(1);
        ModInt mul(x);
        while (p > 0) {
            if (p & 1ul) ret *= mul;
            mul *= mul;
            p >>= 1ul;
        }
        return ret;
    }
};

const int64_t MOD = 1000000007LL;
using mint = ModInt<MOD>;

template<class T> class Fenwick {
private:
    vector<T> dat;
    int n;
public:
    Fenwick(int _n) : dat(_n + 1), n(_n) {}
    // sum of [1, i]
    T sum(int i) {
        T s = 0;
        while(i > 0) s += dat[i], i -= i & -i;
        return s;
    }
    // sum of [l, r]
    T sum(int l, int r) {
        return l > r ? 0 : sum(r) - sum(l - 1);
    }
    void add(int i, T x) {
        while(i <= n) dat[i] += x, i += i & -i;
    }
};

int main() {
    int N, d, K;
    cin >> N >> d >> K;
    const int M = 90009;
    using FEN = Fenwick<mint>;
    vector<FEN> fen(N + 1, FEN(M + 2));
    fen[0].add(1, 1);
    for(int i = 1; i <= N; ++i) {
        for(int j = 1; j <= M; ++j) {
            fen[i].add(j + 1, fen[i - 1].sum(max(0, j - d) + 1, j));
        }
    }
    cout << fen[N].sum(K + 1, K + 1) << '\n';
    return 0;
}
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