组合数取合数mod

版权声明：是自己手打的没错 https://blog.csdn.net/Mr_Treeeee/article/details/82194285

using namespace std;
 
const int MAXN = 200005;
 
bool ispri[MAXN];
int prime[MAXN];
int priCnt;
 
void CalPrime()
{
    priCnt = 0;
    memset(ispri,false,sizeof(ispri));
 
    for(int i = 2;i < MAXN; ++i)
    {
        if(ispri[i] == false)
        {
            prime[priCnt++] = i;
            for(int j = i+i;j < MAXN; j += i)
                ispri[j] = true;
        }
    }
}
 
LL DivideByPrime(LL N,LL P)
{
    LL ans = 0;
 
    while(N)
        ans += N/P,N /= P;
 
    return ans;
}
 
LL QuickMod(LL a,LL b,LL m)
{
    LL ans = 1;
    a %= m;
    while(b)
    {
        if(b&1)
            ans = ans*a%m,b--;
        b >>= 1;
        a = a*a%m;
    }
    return ans;
}
 
//C(N,M) % P
LL CalCnmModP(LL N,LL M,LL P)
{
    LL ans = 1;
    for(int i = 0 ;i < priCnt && prime[i] <= N; ++i)
    {
        LL x = DivideByPrime(N,prime[i]);
        LL y = DivideByPrime(N-M,prime[i]);
        LL z = DivideByPrime(M,prime[i]);
 
        x -= (y+z);
 
        ans *= QuickMod(prime[i],x,P);
        ans %= P;
    }
    return ans;
}