nCr mod M.cpp

#include <bits/stdc++.h>

using namespace std;

#define MOD 1000000007
#define MAX 1200006
#define ll long long
ll fact[MAX], Inv[MAX];

ll bigMod(ll n,ll r){
    if(r==0) return 1LL;
    ll ret=bigMod(n,r/2);
    ret=(ret*ret)%MOD;
    if(r%2==1) ret=(ret*n)%MOD;
    return ret;
}

void pre()
{
    fact[0] = Inv[0] = 1;
    for(int i=1; i<MAX; i++){
        fact[i] = (fact[i-1]*i)%MOD;
        Inv[i] = bigMod(fact[i], MOD-2);
    }
}

ll nCr(ll n, ll r)
{
    return (fact[n] * ((Inv[r]*Inv[n-r])%MOD)) %MOD;
}

int main()
{
    pre();
}