卢卡斯定理

卢卡斯定理

ll fac[N];
ll fast_pow(ll a, ll n){
    ll ans = 1;
    a %= mod;
    while(n){
        if(n&1){
            ans = (ans * a) % mod;
        }
        a = (a * a) % mod;
        n >>= 1;
    }
    return ans;
}
ll inverse(ll a){
    return fast_pow(a, mod - 2);
}
ll C(ll n, ll r){
    if(r > n) return 0;
    return ((fac[n] * inverse(fac[r])) % mod * inverse(fac[n - r]) % mod);
}
ll Lucas(ll n, ll r){
    if(r == 0) return 1;
    return C(n % mod, r % mod) * Lucas(n/mod, r/mod) % mod;
}

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还有没写出来的拓展卢卡斯: