[数学杂题] POJ3761 Bubble Sort

#include<cstdio>#include<algorithm>using namespace std;typedef long long LL;const LL maxn=1000015, MOD=20100713;LL fac[maxn];int Pow(int a,int b){    LL res=1;    for(LL w=a%MOD;b;b>>=1,w=w*w%MOD) if(b&1) res=(res*w)%MOD;    return res;}int n,m,_test;int main(){    fac[0]=1; for(int i=1;i<=1000005;i++) fac[i]=fac[i-1]*i%MOD;    scanf("%d",&_test);    while(_test--){        scanf("%d%d",&n,&m);        if(!m){ printf("1\n"); continue; }        printf("%lld\n", (fac[m]*Pow(m+1,n-m)%MOD - fac[m-1]*Pow((m-1)+1,n-(m-1))%MOD +MOD)%MOD );    }    return 0;}