Submission #5327329

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Source Code Expand

#include<bits/stdc++.h>
using namespace std;

#define int long long
#define endl "\n"
#define REP(i,a,n) for(int i=a;i<n;++i)
#define RUP(a,b) ((a+b-1)/(b))
#define SORTG(v) sort(v.begin(),v.end(),greater<>())
#define SORT(v) sort(v.begin(),v.end())
#define ALL(v) (v).begin(),(v).end()
#define pb push_back
#define mp make_pair
#define mt make_tuple
#define MOD 1000000007
#define INF LLONG_MAX/3

typedef long long ll;
typedef pair<int,int> Pii;
typedef tuple<int,int,int> Tiii;
typedef vector<int> Vi;
typedef vector<Vi> VVi;
typedef vector<string> Vs;

template<class T> void chmax(T& a, T b) {if(a<b){a=b;}}
template<class T> void chmin(T& a, T b) {if(a>b){a=b;}}
void YesNo(int a) {if(a){cout<<"Yes"<<endl;}else{cout<<"No"<<endl;}}
void YESNO(int a) {if(a){cout<<"YES"<<endl;}else{cout<<"NO"<<endl;}}
void AorB(int a,string b,string c) {if(a){cout<<b<<endl;}else{cout<<c<<endl;}}
int gcd(int a,int b){return b?gcd(b,a%b):a;}
void start(){cin.tie(0);cout.tie(0);ios::sync_with_stdio(false);}

const int MAX = 510000;
long long fac[MAX], finv[MAX], inv[MAX];

// テーブルを作る前処理
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 % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD / i) % MOD;
        finv[i] = finv[i - 1] * inv[i] % MOD;
    }
}

// 二項係数計算
long long COM(int n, int k){
    if (n < k) return 0;
    if (n < 0 || k < 0) return 0;
    return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}

signed main(){start();
    int n,k;
    cin>>n>>k;
    COMinit();
    if(n>k) cout<< COM(n+k-1,k)<<endl;
    else cout << COM(n,k%n)<< endl;
    return 0;
}

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