Submission #1304773

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Source Code Expand

#include <bits/stdc++.h>
using namespace std;
#define int long long
using ll=long long;
using vi=vector<int>;
using vl=vector<long long>;
using pii=pair<int,int>;
using pll=pair<long long,long long>;
#define ITR(i,c) for(auto i=begin(c);i!=end(c);++i)
#define FORE(x,c) for(auto &x:c)
#define REPF(i,a,n) for(int i=a,i##len=(int)(n);i<i##len;++i)
#define REP(i,n) REPF(i,0,n)
#define REPR(i,n) for(int i=(int)(n);i>=0;--i)
#define REPW(i,n) for(i=0;i<(int)(n);++i)
#define ALL(c) begin(c),end(c)
#define RALL(c) rbegin(c),rend(c)   // c++14
#define SZ(c) ((int)c.size())
#define EXIST(c,x) (c.find(x)!=end(c))
#define OUTOFRANGE(y,x,h,w) (y<0||x<0||y>=h||x>=w)
#define dump(...)
const int DX[9]={0,1,0,-1,1,1,-1,-1,0},DY[9]={-1,0,1,0,-1,1,1,-1,0};
#define INF (1001001001)
#define INFLL (1001001001001001001ll)
template<class T> ostream& operator << (ostream &os,const vector<T> &v) {
    ITR(i,v) os << *i << (i==end(v)-1 ? "" : "\n"); return os; }
template<class T> istream& operator >> (istream &is,vector<T> &v) {
    ITR(i,v) is >> * i; return is; }
template<class T> istream& operator >> (istream &is, pair<T,T> &p) {
        is >> p.first >> p.second; return is; }
template<class T>bool chmax(T &a,const T &b){if(a<b){a=b;return 1;}return 0;}
template<class T>bool chmin(T &a,const T &b){if(b<a){a=b;return 1;}return 0;}
//------------------------------------------------------------------------------
struct before_main_function {
    before_main_function() {
        #ifdef int
            #undef INF
            #define INF INFLL
            #define stoi stoll
        #endif
        cin.tie(0);ios::sync_with_stdio(false);
        cout<<setprecision(15)<<fixed;
    }
} before_main_function;
//------------------------------------------------------------------------------

const int MOD=1e9+7;
const int MAX_N=300000;
ll fact[MAX_N+1];
ll fact_inv[MAX_N+1];
ll mod_pow(ll a,ll b) {
    if(a==0) return 1;
    a%=MOD;
    ll product=1;
    while(b>0) {
        if(b&1) {
            product*=a;
            product%=MOD;
        }
        a*=a;
        a%=MOD;
        b>>=1;
    }
    return product%MOD;
}
inline ll nCr_mod(ll n,ll r) {
    ll ret = fact[n] * fact_inv[r] % MOD * fact_inv[n-r] % MOD;
    return ret;
}
void init_fact() {
    fact[0]=1, fact_inv[0]=1;
    REPF(i,1,MAX_N) {
        fact[i]=(fact[i-1]*i)%MOD;
        fact_inv[i]=mod_pow(fact[i],MOD-2);
    }
}
signed main() {
    init_fact();
    int N,K;
    cin>>N>>K;
    if(N>K) {
        cout<<nCr_mod(N+K-1,K)<<endl;    
    }
    else {
        cout<<nCr_mod(N,K%N)<<endl;
    }
    return 0;
}

Submission Info

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