結果

問題 No.1011 Infinite Stairs
ユーザー rniya
提出日時 2020-03-20 21:45:16
言語 C++14
(gcc 13.3.0 + boost 1.87.0)
結果
AC  
実行時間 310 ms / 2,000 ms
コード長 3,877 bytes
コンパイル時間 1,820 ms
コンパイル使用メモリ 173,100 KB
実行使用メモリ 227,564 KB
最終ジャッジ日時 2024-07-17 11:47:04
合計ジャッジ時間 4,226 ms
ジャッジサーバーID
（参考情報） 		judge5 / judge1
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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;
typedef long long ll;
const ll MOD=1e9+7;

template<uint_fast64_t Modulus> class modint{
    using u64=uint_fast64_t;
    public:
    u64 a;
    constexpr modint(const u64 x=0) noexcept:a(((x%Modulus)+Modulus)%Modulus){}
    constexpr u64 &value() noexcept{return a;}
    constexpr const u64 &value() const noexcept{return a;}
    constexpr modint &operator+=(const modint &rhs) noexcept{
        a+=rhs.a;
        if (a>=Modulus) a-=Modulus;
        return *this;
    }
    constexpr modint operator+(const modint &rhs) const noexcept{
        return modint(*this)+=rhs;
    }
    constexpr modint &operator++() noexcept{
        return ++a,*this;
    }
    constexpr modint operator++(int) noexcept{
        modint t=*this; return ++a,t;
    }
    constexpr modint &operator-=(const modint &rhs) noexcept{
        if (a<rhs.a) a+=Modulus;
        a-=rhs.a;
        return *this;
    }
    constexpr modint operator-(const modint &rhs) const noexcept{
        return modint(*this)-=rhs;
    }
    constexpr modint &operator--() noexcept{
        return --a,*this;
    }
    constexpr modint operator--(int) noexcept{
        modint t=*this; return --a,t;
    }
    constexpr modint &operator*=(const modint &rhs) noexcept{
        a=a*rhs.a%Modulus;
        return *this;
    }
    constexpr modint operator*(const modint &rhs) const noexcept{
        return modint(*this)*=rhs;
    }
    constexpr modint &operator/=(modint rhs) noexcept{
        u64 exp=Modulus-2;
        while(exp){
            if (exp&1) *this*=rhs;
            rhs*=rhs; exp>>=1;
        }
        return *this;
    }
    constexpr modint operator/(const modint &rhs) const noexcept{
        return modint(*this)/=rhs;
    }
    constexpr modint operator-() const noexcept{
        return modint(Modulus-a);
    }
    constexpr bool operator==(const modint &rhs) const noexcept{
        return a==rhs.a;
    }
    constexpr bool operator!=(const modint &rhs) const noexcept{
        return a!=rhs.a;
    }
    constexpr bool operator!() const noexcept{return !a;}
    friend constexpr modint pow(modint rhs,long long exp) noexcept{
        modint res{1};
        while(exp){
            if (exp&1) res*=rhs;
            rhs*=rhs; exp>>=1;
        }
        return res;
    }
    template<class T> friend constexpr modint operator+(T x,modint y) noexcept{
        return modint(x)+y;
    }
    template<class T> friend constexpr modint operator-(T x,modint y) noexcept{
        return modint(x)-y;
    }
    template<class T> friend constexpr modint operator*(T x,modint y) noexcept{
        return modint(x)*y;
    }
    template<class T> friend constexpr modint operator/(T x,modint y) noexcept{
        return modint(x)/y;
    }
    friend ostream &operator<<(ostream &s,const modint &rhs) noexcept {
        return s << rhs.a;
    }
    friend istream &operator>>(istream &s,modint &rhs) noexcept {
        u64 a; rhs=modint{(s >> a,a)}; return s;
    }
};

using mint=modint<MOD>;

const int MAX=5e5+10;
vector<mint> fac(MAX),finv(MAX),inv(MAX);
void COMinit(){
    fac[0]=fac[1]=1;
    finv[0]=finv[1]=1;
    inv[1]=1;
    for (int i=2;i<MAX;++i){
        fac[i]=fac[i-1]*i;
        inv[i]=-inv[MOD%i]*(MOD/i);
        finv[i]=finv[i-1]*inv[i];
    }
}
mint COM(int n,int k){
    if (n<k||n<0||k<0) return 0;
    return fac[n]*finv[k]*finv[n-k];
}

//Be careful with the value of MAX and conducting COMinit()

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    int N,d,K; cin >> N >> d >> K;
    vector<vector<mint>> dp(N+1,vector<mint>(K+1,0));
    vector<mint> sum(K+2,1);
    dp[0][0]=1; sum[0]=0;
    for (int i=0;i<N;++i){
        for (int j=K;j>=0;--j){
            dp[i+1][j]+=sum[j]-sum[max(0,j-d)];
            sum[j+1]=dp[i+1][j];
        }
        for (int j=0;j<K+1;++j) sum[j+1]+=sum[j];
    }
    cout << dp[N][K] << '\n';
}
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