HDU 6093 Rikka with Number

#include<bits/stdc++.h>
using namespace std;

const int MAXN=5050;
const long long mod=998244353;
char ch[MAXN];
double L[MAXN];
int I[MAXN],A[MAXN],B[MAXN],C[MAXN],pd[MAXN];
int x[MAXN],y[MAXN],lenx,leny;
int len,le;

void change(int len,int m)
{
int x,pre,i;
le=0;
memcpy(B,A,sizeof(A));
while(len)
{
x=0;
for(i=len;i;i--)
{
pre=x;
x=(x*10+B[i])%m;
B[i]=(pre*10+B[i])/m;
}
C[++le]=x;
while(len&&B[len]==0)
len--;
}
}

int calc(int m)
{
change(len,m);
if(le>m)
return (I[m]-I[m-1]+mod)%mod;
if(le<m)
return 0;
int i,j,ans;
for(i=0;i<m;i++)
pd[i]=0;
ans=0;
for(i=1;i<C[le];i++)
ans=(ans+I[le-1])%mod;
pd[C[le]]=1;
for(i=le-1;i>0;i--)
{
for(j=0;j<C[i];j++)
{
if(pd[j]==0)
ans=(ans+I[i-1])%mod;
}
if(pd[C[i]])
break;
pd[C[i]]=1;
if(i==1)
ans=(ans+1)%mod;
}
return ans;
}

int calc()
{
if(len==0)
return 0;
int ans,where,i;
ans=0;
where=2;
while(L[where]<=len-1)
where++;
if(where<=15)
{
for(i=2;i<=15;i++)
ans=(ans+calc(i))%mod;
return ans;
}
for(i=2;i<=where-2;i++)
ans=((ans+I[i]-I[i-1])%mod+mod)%mod;
ans=(ans+calc(where-1)+calc(where))%mod;
return ans;
}

int main()
{
int i,T,lenx,ans;
len=1;
while(L[len]<MAXN)
{
len++;
L[len]=log(len)/log(10)*(len-1);
}
I[0]=1;
for(i=1;i<MAXN;i++)
I[i]=I[i-1]*1ll*i%mod;
scanf("%d",&T);
while(T--)
{
scanf("%s",ch+1);
len=strlen(ch+1);
for(i=1;i<=len;i++)
A[i]=ch[len-i+1]-'0';
lenx=len;
for(i=1;i<=len;i++)
x[i]=A[i];
A[1]--;
for(i=1;i<=len;i++)
{
if(A[i]<0)
{
A[i+1]--;
A[i]+=10;
}
}
while(len&&A[len]==0)
len--;
ans=calc();
scanf("%s",ch+1);
len=strlen(ch+1);
for(i=1;i<=len;i++)
A[i]=ch[len-i+1]-'0';
leny=len;
for(i=1;i<=len;i++)
y[i]=A[i];
ans=(calc()-ans+mod)%mod;
printf("%d\n",ans);
}
}