[BZOJ3670] Zoo extension KMP

First use extended KMP to find$S_{i..n}$and$S$LCP$next_{i}$.
Consider each suffix$S_{i..n}$all prefixes of$S_{i..k}$right$num_k$contributed, contributed$k$obviously in a range$[i,\min(2i-1,i+next_i)-1]$, add and subtract in the difference array, and finally prefix the sum.
Code:

#include<iostream> 
#include<cstdio>
#include<cstring>
#define N 1000010
#define ll long long
using namespace std;
const int mod=1000000007;
int n,nxt[N],xxx[N];
char s[N];
void ex_kmp()
{
    memset(nxt,0,sizeof(nxt));
    int st=2,ed=1;
    while(ed<n&&s[ed]==s[ed+1]) ed++;
    nxt[2]=ed-1;
    nxt[1]=n;
    for(int i=3;i<=n;i++)
    {
        if(nxt[i-st+1]<ed-i+1) {nxt[i]=nxt[i-st+1];continue;}
        if(ed<i) ed=i-1,st=i;
        for(int j=ed-i+1;ed<n&&s[ed+1]==s[j+1];j++,ed++);
        st=i;nxt[i]=max(ed-i+1,0);
    }
}
int main()
{
    int ca;
    scanf("%d",&ca);
    while(ca--)
    {
        scanf("%s",s+1);
        n=strlen(s+1);
        ex_kmp();
        memset(xxx,0,sizeof(xxx));  
        for(int i=1;i<=n;i++)
            xxx[i]++,xxx[min(2*i-1,i+nxt[i])]--;
        ll ans=1,cnt=0;
        for(int i=1;i<=n;i++)
            cnt+=xxx[i],ans=ans*(cnt+1)%mod;
        printf("%lld\n",ans);
    }
    return 0;
}