繁华模拟赛 Vincent的城堡

#include<iostream>

#include<cstdio>

#include<string>

#include<cstring>

#include<algorithm>

#define ll long long

using namespace std;

const ll mod = ;

ll n,k,c[][];

ll ansa,ansb,ans;

void get_c(){

    for(int i = ;i <= ;i++){

        c[i][] = c[i][i] = ;

        c[i][] = c[i][i-] = i;

    }

    for(int i = ;i <= ;i++){

        for(int j = ;j < i;j++){

            c[i][j] = c[i-][j-] + c[i-][j];

        }

    }

}

ll q_mul(ll a,ll b){

    ll ans = ;

    while(b){

        if(b&){

            ans = (ans + a) % mod;

        }

        a = (a + a) % mod;

        b >>= ;

    }

    return ans;

}

ll q_pow(ll a,ll b){

    ll ans = ;

    while(b){

        if(b&){

            ans = q_mul(ans,a);

        }

        a = q_mul(a,a);

        b >>= ;

    }

    return ans;

}

int main(){

    freopen("castle.in","r",stdin);

    freopen("castle.out","w",stdout);

    cin>>n>>k;

    get_c();

    ansb = q_pow(n-k,n-k);

    ansa = q_pow(k,k-);//诡异结论

    ans = q_mul(ansa,ansb);

    cout<<ans;

    return ;

}