[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\n",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 }