[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：

#include<cstdio>
#include<iostream>
#include<cstring>
#include<algorithm>
#define maxn 300005 
using namespace std;
typedef long long int64;
char s[maxn];
struct ptree{
    int n,last,idx,s[maxn],son[maxn][26],fai[maxn],len[maxn],cnt[maxn];
    void init(){n=0,s[0]=-1,idx=1,last=0,fai[0]=1,len[1]=-1;}
    int get_fai(int x){
        while (s[n-len[x]-1]!=s[n]) x=fai[x];
        return x;
    }
    void insert(int ch){
        s[++n]=ch;
        int p=get_fai(last);
        if (!son[p][ch]){
            len[++idx]=len[p]+2;
            int q=idx;
            fai[q]=son[get_fai(fai[p])][ch];
            son[p][ch]=q;
        }
        cnt[last=son[p][ch]]++;
    }
    void count(){for (int i=idx;i>=0;i--) cnt[fai[i]]+=cnt[i];}
    void query(){
        int64 ans=0;
        count();
        for (int i=0;i<=idx;i++) ans=max(ans,1LL*cnt[i]*len[i]);
        printf("%lld
",ans); 
    } 
}T;
int main(){
    scanf("%s",s+1); T.init();
    for (int i=1;s[i];i++) T.insert(s[i]-'a');
    T.query(); 
    return 0;
}