对于100%的数据，n<=1000000

 1 #include<cstring>
 2 #include<cstdio>
 3 #include<algorithm>
 4 #include<iostream>
 5 #include<cmath>
 6 #include<queue>
 7 #include<vector>
 8
 9 #define N 1000007
10 #define mod 1000000007
11 #define fzy pair<int,int>
12 using namespace std;
13 inline int read()
14 {
15     int x=0,f=1;char ch=getchar();
16     while(!isdigit(ch)){if(ch=='-')f=-1;ch=getchar();}
17     while(isdigit(ch)){x=(x<<1)+(x<<3)+ch-'0';ch=getchar();}
18     return x*f;
19 }
20
21 int n,m;
22 int i,r,p,f[N<<1],fa[N],vis[N],ans=1;
23 char a[N],s[N<<1],col[N];
24 struct E{
25     int v;
26     E*nxt;
27 }*j,*h[N],pool[N<<1],*cur=pool;
28
29 int find(int x)
30 {
31     return fa[x]==x?x:fa[x]=find(fa[x]);
32 }
33 inline void merge(int x,int y)
34 {
35       if(x&1)return;
36       if(find(x>>=1)==find(y>>=1))return;
37       fa[fa[x]]=fa[y];
38 }
39 inline void add(int x,int y)
40 {
41       if(!x||!y||x&1)return;
42       j=cur++;j->v=y>>1;j->nxt=h[x>>=1];h[x]=j;
43 }
44 int main()
45 {
46       scanf("%s",a+1),n=strlen(a+1);
47       for(i=1;i<=n;i++)
48           fa[i]=i;
49       for(i=1;i<=n;i++)
50           s[i<<1]=a[i],s[i<<1|1]='#';
51     s[0]='$',s[1]='#',s[m=(n+1)<<1]='@';
52       for(f[1]=1,i=2;i<m;i++)
53     {
54         for(f[i]=r>i?min(r-i,f[p*2-i]):1;s[i-f[i]]==s[i+f[i]];f[i]++) merge(i+f[i],i-f[i]);
55         add(i+f[i],i-f[i]);
56         if(i+f[i]>r)r=i+f[i],p=i;
57       }
58       for(i=1;i<=n;i++)
59           if(!col[find(i)])
60         {
61             for(p=26,j=h[i];j;j=j->nxt)
62                 if(col[find(j->v)]) if(vis[fa[j->v]]<i) vis[fa[j->v]]=i,p--;
63             col[fa[i]]=1,ans=1LL*ans*p%1000000007;
64           }
65       printf("%d",ans);
66 }