bzoj4872: [Shoi2017]分手是祝愿

一早上膝盖跪烂了ORZ出门右转膜题解谢谢

#include<cstdio>
#include<iostream>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<cmath>
using namespace std;
typedef long long LL;
const int mod=100003;

LL fac[110000],inv[110000];
int a[110000];LL f[110000];
int main()
{
    fac[1]=1,inv[1]=1;
    for(int i=2;i<=105000;i++)fac[i]=fac[i-1]*i%mod,inv[i]=(mod-mod/i)*inv[mod%i]%mod;
    
    int n,k,num=0;
    scanf("%d%d",&n,&k);
    for(int i=1;i<=n;i++)scanf("%d",&a[i]);
    for(int i=n;i>=1;i--)
        if(a[i]==1)
        {
            for(int j=1;j*j<=i;j++)
                if(i%j==0)
                {
                    a[j]^=1;
                    if(j*j!=i)a[i/j]^=1;
                }
            num++;
        }
    if(num<=k){printf("%d\n",num*fac[n]%mod);return 0;}
    
    LL ans=0;f[n]=1;
    for(int i=n-1;i>k;i--)f[i]=(n+(n-i)*f[i+1])%mod*inv[i]%mod;
    for(int i=num;i>k;i--)ans=(ans+f[i])%mod;
    ans=(ans+k)%mod;
    
    printf("%d\n",ans*fac[n]%mod);
    return 0;
}