poj 3761 bubble sort (排列组合)

#include<cstdio>
#include<cstring>
#define ll long long
#define mod 20100713
const int maxn=;
ll a[maxn];

ll poww(ll x,int n)
{
    ll ret=;
    while(n)
    {
        if(n&)
            ret=ret*x%mod;
        n>>=;
        x=x*x%mod;
    }
    return ret;
}

int main()
{
    a[]=;
    for(int i=;i<maxn;i++)
        a[i]=a[i-]*i%mod;
    int T;
    scanf("%d",&T);
    while(T--)
    {
        int n,k;
        scanf("%d%d",&n,&k);
        ll ans=a[k]*(poww(k+,n-k)-poww(k,n-k)+mod)%mod;
        printf("%lld\n",ans);
    }
    return ;
}