LightOJ 1067 - Combinations【Lucas定理】

#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <algorithm>
#include <string.h>
#include <iostream>

using namespace std;

const long long MOD = 1000003;

long long pow(long long a, long long b, long long c)
{
long long tmp = 1;
while (b)
{
if (b & 1) tmp = (tmp*a) % c;
a = (a*a) % c;
b >>= 1;
}
return tmp;
}

long long fac[1000005];

void get_fac(long long p)
{
fac[0] = 1;
for (int i = 1;i <= p;i++)
fac[i] = (fac[i - 1] * i) % p;
}

long long Lucas(long long n, long long m, long long p)
{
long long tmp = 1;
while (n && m)
{
long long a = n%p, b = m%p;
if (a < b) return 0;
tmp = (tmp * fac[a] * pow(fac[b] * fac[a - b] % p, p - 2, p)) % p;

n /= p;
m /= p;
}
return tmp;
}

int n, m;

int main()
{
get_fac(MOD);
int T;
scanf("%d", &T);
for (int t = 1;t <= T;t++)
{
scanf("%d %d", &n, &m);
int ans = Lucas(n, m, MOD);
printf("Case %d: %d\n", t, ans);
}
return 0;
}