[Apio2014]回文串

http://www.lydsy.com:808/JudgeOnline/problem.php?id=3676

这是一道回文树裸题，具体如何建图见http://blog.csdn.net/u013368721/article/details/42100363

code：

 1 #include<cstdio>
 2 #include<iostream>
 3 #include<cstring>
 4 #include<algorithm>
 5 #define maxn 300005 
 6 using namespace std;
 7 typedef long long int64;
 8 char s[maxn];
 9 struct ptree{
10     int n,last,idx,s[maxn],son[maxn][26],fai[maxn],len[maxn],cnt[maxn];
11     void init(){n=0,s[0]=-1,idx=1,last=0,fai[0]=1,len[1]=-1;}
12     int get_fai(int x){
13         while (s[n-len[x]-1]!=s[n]) x=fai[x];
14         return x;
15     }
16     void insert(int ch){
17         s[++n]=ch;
18         int p=get_fai(last);
19         if (!son[p][ch]){
20             len[++idx]=len[p]+2;
21             int q=idx;
22             fai[q]=son[get_fai(fai[p])][ch];
23             son[p][ch]=q;
24         }
25         cnt[last=son[p][ch]]++;
26     }
27     void count(){for (int i=idx;i>=0;i--) cnt[fai[i]]+=cnt[i];}
28     void query(){
29         int64 ans=0;
30         count();
31         for (int i=0;i<=idx;i++) ans=max(ans,1LL*cnt[i]*len[i]);
32         printf("%lld
",ans); 
33     } 
34 }T;
35 int main(){
36     scanf("%s",s+1); T.init();
37     for (int i=1;s[i];i++) T.insert(s[i]-'a');
38     T.query(); 
39     return 0;
40 }