procon

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:heavy_check_mark: test/AOJ_DPL_5_G.test.cpp

Depends on

Code

#define PROBLEM "http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=DPL_5_G"

#include "../template.hpp"

#include "../type/modint.hpp"

#include "../Math/Precalc.hpp"

using mint=ModInt<1000000007>;

Precalc<mint> F(500000);

/*
玉: 区別する
箱: 区別しない
入れ方: 制限なし

ベル数
https://ja.wikipedia.org/wiki/%E3%83%99%E3%83%AB%E6%95%B0
*/

signed main(){
    int n,k;cin>>n>>k;
    cout<<F.Bell_number(n,k)<<endl;
    return 0;
}
#line 1 "test/AOJ_DPL_5_G.test.cpp"
#define PROBLEM "http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=DPL_5_G"

#line 1 "template.hpp"
#include<bits/stdc++.h>
using namespace std;
#define ALL(x) begin(x),end(x)
#define rep(i,n) for(int i=0;i<(n);i++)
#define debug(v) cout<<#v<<":";for(auto x:v){cout<<x<<' ';}cout<<endl;
#define mod 1000000007
using ll=long long;
const int INF=1000000000;
const ll LINF=1001002003004005006ll;
int dx[]={1,0,-1,0},dy[]={0,1,0,-1};
// ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
template<class T>bool chmax(T &a,const T &b){if(a<b){a=b;return true;}return false;}
template<class T>bool chmin(T &a,const T &b){if(b<a){a=b;return true;}return false;}

struct IOSetup{
    IOSetup(){
        cin.tie(0);
        ios::sync_with_stdio(0);
        cout<<fixed<<setprecision(12);
    }
} iosetup;
 
template<typename T>
ostream &operator<<(ostream &os,const vector<T>&v){
    for(int i=0;i<(int)v.size();i++) os<<v[i]<<(i+1==(int)v.size()?"":" ");
    return os;
}
template<typename T>
istream &operator>>(istream &is,vector<T>&v){
    for(T &x:v)is>>x;
    return is;
}

#line 4 "test/AOJ_DPL_5_G.test.cpp"

#line 1 "type/modint.hpp"
template<int Mod>
struct ModInt{
    int x;
    ModInt():x(0){}
    ModInt(int y): x (y >= 0 ? y % Mod : (Mod - (-y) % Mod) % Mod){}
    ModInt(long long y){
        if (y >= 0)
        {
            x = (int)(y % (ll)(Mod));
        }
        else
        {
            int tmp = (int)((-y) % (ll)Mod);
            x = (Mod - tmp) % Mod;
        }
    }
    ModInt &operator+=(const ModInt &p){
        if((x += p.x) >= Mod) x -= Mod;
        return *this;
    }
    ModInt &operator-=(const ModInt &p){
        if((x += Mod - p.x) >= Mod) x -= Mod;
        return *this;
    }
    ModInt &operator*=(const ModInt &p){
        x = (int)(1ll * x * p.x % Mod);
        return *this;
    }
    ModInt &operator/=(const ModInt &p){
        (*this) *= p.inverse();
        return *this;
    }
    ModInt operator-()const{return ModInt(-x);}
    ModInt operator+(const ModInt &p)const{return ModInt(*this)+=p;}
    ModInt operator-(const ModInt &p)const{return ModInt(*this)-=p;}
    ModInt operator*(const ModInt &p)const{return ModInt(*this)*=p;}
    ModInt operator/(const ModInt &p)const{return ModInt(*this)/=p;}
    bool operator==(const ModInt &p)const{return x==p.x;}
    bool operator!=(const ModInt &p)const{return x!=p.x;}
    ModInt inverse()const{
        int a = x, b = Mod ,u = 1, v = 0, t;
        while(b>0){
            t=a/b;
            swap(a-=t*b,b);swap(u-=t*v,v);
        }
        return ModInt(u);
    }
    ModInt pow(long long n)const{
        ModInt ret(1),mul(x);
        while(n>0){
            if(n&1) ret*=mul;
            mul*=mul;n>>=1;
        }
        return ret;
    }
    friend ostream &operator<<(ostream &os,const ModInt &p){return os<<p.x;}
    friend istream &operator>>(istream &is,ModInt &a){long long t;is>>t;a=ModInt<Mod>(t);return (is);}
    static int get_mod(){return Mod;}
};
#line 6 "test/AOJ_DPL_5_G.test.cpp"

#line 1 "Math/Precalc.hpp"
template<typename T>
struct Precalc{
    vector<T> fact,finv,inv;
    int Mod;
    Precalc(int MX):fact(MX),finv(MX),inv(MX),Mod(T::get_mod()){
        fact[0]=T(1),fact[1]=T(1),finv[0]=T(1),finv[1]=T(1),inv[1]=T(1);
        for(int i=2;i<MX;i++){
            fact[i]=fact[i-1]*T(i);
            inv[i]=T(0)-inv[Mod%i]*(T(Mod/i));
            finv[i]=finv[i-1]*inv[i];
        }
    }
    T com(int n,int k){
        if(n<k) return T(0);
        if(n<0 or k<0) return T(0);
        return fact[n]*(finv[k]*finv[n-k]);
    }
    T fac(int n){
        return fact[n];
    }
    // 重複組み合わせ:n種類の物から重複を許し，k個選ぶ
    T nHk(int n,int k){
        return com(n+k-1,k);
    }
    // 玉n区別，箱k区別，各箱1個以上O(k)
    T F12_dis_dis_one(int n,int k){
        if(n<k)return T(0);
        T ret=0;
        for(int i=0;i<=k;i++){
            T add=com(k,i)*(T(i).pow(n));
            if((k-i)%2) ret-=add;
            else        ret+=add;
        }
        return ret;
    }
    // 区別できるn人をkチームにわける，チームには最低1人属する
    // ベン図をイメージ, 包除
    // require : T(num).pow(k)
    T Stirling_number(int n,int k){
        T ret=0;
        for(int i=0;i<=k;i++) ret+=com(k,i)*T(i).pow(n)*((k-i)%2?(-1):1);
        return ret/T(fac(k));
    }
    // 区別できるn人をkチーム以下にわける
    T Bell_number(int n,int k){
        T ret=0;
        for(int i=1;i<=k;i++) ret+=Stirling_number(n,i);
        return ret;
    }
    T partition_function(int n,int k){
        auto table=partition_function_table(n,k);
        return table[n][k];
    }
    vector<vector<T>> partition_function_table(int n,int k){
        vector<vector<T>> ret(n+1,vector<T>(k+1,0));
        ret[0][0]=1;
        for(int i=0;i<=n;i++)for(int j=1;j<=k;j++)if(i or j){
            ret[i][j]=ret[i][j-1];
            if(i-j>=0) ret[i][j]+=ret[i-j][j];
        }
        return ret;
    }
    // n = y.size - 1
    // n次の多項式f, f(0), f(k)の値がわかっていればf(t)が求まる
    // 1^k + ... n^k はk+1次多項式，k=1ならn(n+1)/2
    T LagrangePolynomial(vector<T> y,long long t){
        int n=(int)y.size()-1;
        if(t<=n) return y[t];
        T ret=T(0);
        vector<T> l(n+1,1),r(n+1,1);
        for(int i=0;i<n;i++) l[i+1]=l[i]*(t-i);
        for(int i=n;i>0;i--) r[i-1]=r[i]*(t-i);
        for(int i=0;i<=n;i++){
            T add=y[i]*l[i]*r[i]*finv[i]*finv[n-i];
            ret+=((n-i)%2?-add:add);
        }
        return ret;
    }
    /* sum combination(n+x, x), x=l to r
       https://www.wolframalpha.com/input/?i=sum+combination%28n%2Bx+%2Cx%29%2C+x%3Dl+to+r&lang=ja 
       check n+x < [COM_PRECALC_MAX]    */
    T sum_of_comb(int n,int l,int r){
        if(l>r)return T(0);
        T ret=T(r+1)*com(n+r+1,r+1)-T(l)*com(l+n,l);
        ret/=T(n+1);
        return ret;
    }

    /* 
    - sum of comb 2
        https://www.wolframalpha.com/input/?i=sum+combination%28i%2Bj%2Ci%29%2C+i%3D0+to+a-1%2C+j%3D0+to+b-1&lang=ja
        https://yukicoder.me/problems/no/1489
        
        sum binom(i+j,i) i=0 to a-1, j=0 to b-1
        = ( binom(a+b,a-1)*(b+1)/a ) - 1
    */

    // +-1をしてXにたどり着くパターン数
    T RandomWalk1D(int X, int N){
        X = abs(X);
        if(X>N or X%2!=N%2) return T(0);

        return com(N, (N+X)/2);
    }

    /*
    O(1)
    https://atcoder.jp/contests/abc240/editorial/3423
    */
    T RandomWalk2D(int X, int Y, int N){
        return RandomWalk1D(X+Y, N)*RandomWalk1D(X-Y, N);
    }
};
#line 8 "test/AOJ_DPL_5_G.test.cpp"

using mint=ModInt<1000000007>;

Precalc<mint> F(500000);

/*
玉: 区別する
箱: 区別しない
入れ方: 制限なし

ベル数
https://ja.wikipedia.org/wiki/%E3%83%99%E3%83%AB%E6%95%B0
*/

signed main(){
    int n,k;cin>>n>>k;
    cout<<F.Bell_number(n,k)<<endl;
    return 0;
}
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