Find the number of combinations (Fermat's little theorem)

#include"iostream"
using namespace std;
const int maxn=1e3+5;
const int MOD=1e9+7;
int inv[maxn];//阶乘的逆元
int fac[maxn];//阶乘
long long ksm(long long a,long long b,long long mod)
{
    long long res=1,base=a;
    while(b)
    {
        if(b&1)res=(res*base)%mod;
        b>>=1;
        base=(base*base)%mod;
    }
    return res;
}
long long C(int n,int m)
{
    if(m==0||n==m)return 1;
    long long res=1;
    res=res*fac[n]%MOD*inv[m]%MOD*inv[n-m]%MOD;
    return res;
}
int main()
{
    fac[0]=fac[1]=inv[1]=1;
    for(long long i=2;i<maxn;i++)
    {
        inv[i]=(inv[i-1]*ksm(i,MOD-2,MOD))%MOD;
        fac[i]=(i*fac[i-1])%MOD;
    }
    int N,M;
    while(cin>>N>>M)
    {
        cout<<C(N,M)<<"\n";
    }
}