Submission #3787057

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Source Code Expand

#include<cstdio>
#include<cstring>
#include<vector>
#include<queue>
#include<algorithm>
#include<cmath>
#include<climits>
#include<string>
#include<set>
#include<numeric>
#include<map>
#include<iostream>
using namespace std;
#define rep(i,n) for(int i = 0;i<((int)(n));i++)
#define reg(i,a,b) for(int i = ((int)(a));i<=((int)(b));i++)
#define irep(i,n) for(int i = ((int)(n)-1);i>=0;i--)
#define ireg(i,a,b) for(int i = ((int)(b));i>=((int)(a));i--)
typedef long long ll;
typedef pair<ll, ll> mp;

/*
重複組合せ（a_iがk個で仕切りがn-1個）
*/

struct Factorial{
	long long N,mod;
	vector<long long> fact,inv;
	long long mod_pow(long long x,long long n){
		long long res=1;
		while(n){
			if(n&1) (res*=x)%=mod;
			(x*=x)%=mod;
			n>>=1;
		}
		return res;
	}
	long long Inverse(long long n){
		return mod_pow(n,mod-2);
	}
	Factorial(){}
	Factorial(long long sn,long long smod){
		N=sn; mod=smod;
		fact.reserve(sn+1); inv.reserve(sn+1);
		//初期化
		fact[0]=1;
		for(int i=1;i<=sn;i++){
			fact[i]=(fact[i-1]*i) % mod;
		}
		inv[sn]=Inverse(fact[sn]);
		for(int i=sn;i>0;i--){
			inv[i-1]=(inv[i]*i) % mod;
		}
	}
	long long Fact(long long n){
		if(n<0)return 0;
		return fact[n];
	}
	long long Inv(long long n){
		if(n<0)return 0;
		return inv[n];
	}
	long long Combination(long long n,long long r){
		if(n<r)return 0;
		if(r<0)return 0;
		if(r==0)return 1;
		long long ans=1;
		ans = (ans*Fact(n)) % mod;
		ans = (ans*Inv(r)) % mod;
		ans = (ans*Inv(n-r)) % mod;
		return ans;
	}
	long long plus(long long a,long long b){
		a%=mod;
		b%=mod;
		return (a+b)%mod;
	}
	long long minus(long long a,long long b){
		a%=mod;
		b%=mod;
		return (a+mod-b)%mod;
	}
	long long mul(long long a,long long b){
		a%=mod;
		b%=mod;
		return (a*b)%mod;
	}
	long long div(long long a,long long b){
		a%=mod;
		b%=mod;
		return (a*Inverse(b))%mod;
	}
};

int main(void){
	ll n,k;
	cin>>n>>k;
	Factorial f(200010,1e9+7);
	cout<<f.Combination(n+k-1,k)<<endl;
	return 0;
}

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