poj 3761 Bubble Sort_快速幂

题意：问你冒泡排序第i次排序，一共排了多少次

套公式K!((K + 1) ^ (N - K) - K ^ (N - K))

#include <iostream>#include<cstdio>#include<cstring>using namespace std;#define LL long long#define N 1000010#define M 20100713LL a[N];int _pow(LL v,int k){LL res=1;while(k){if(k&1){res=res*v;res%=M;}v=v*v;v%=M;k>>=1;}return res;}int main(int argc, char** argv) {int t,i,n,k;a[0]=a[1]=1;for(i=2;i<N;i++)a[i]=a[i-1]*i%M;scanf("%d",&t);while(t--){LL sum=0;scanf("%d%d",&n,&k);sum=(_pow(k+1,n-k)-_pow(k,n-k))%M;if(sum<0)sum+=M;printf("%lld\n",sum*a[k]%M);}return 0;}