BZOJ.3676.[APIO2014]回文串(回文树)
很久之前写(抄)过一个Hash+Manacher的做法,当时十分懵逼=-=
然而是道回文树模板题。
回文树教程可以看这里(真的挺妙的)。
顺便再放上MilkyWay的笔记~
//35100kb 708ms
#include <cstdio>
#include <cstring>
#include <algorithm>
#define gc() getchar()
typedef long long LL;
const int N=3e5+5;
struct Palindromic_Tree
{
int las,tot,son[N][26],len[N],fail[N],val[N];
char s[N];
Palindromic_Tree() {tot=1, fail[0]=1, len[1]=-1, s[0]='$';}
inline int Find(int x,int n)
{
while(s[n-len[x]-1]!=s[n]) x=fail[x];
return x;
}
void Insert(int c,int n)
{
int p=Find(las,n);
if(!son[p][c])
{
int np=++tot; fail[np]=son[Find(fail[p],n)][c];
son[p][c]=np, len[np]=len[p]+2;
}
++val[las=son[p][c]];
}
void Solve()
{
scanf("%s",s+1); int n=strlen(s+1);
for(int i=1; i<=n; ++i) Insert(s[i]-'a',i);
LL ans=0;
for(int i=tot; i>1; --i)
val[fail[i]]+=val[i], ans=std::max(ans,1ll*val[i]*len[i]);
printf("%lld\n",ans);
}
}T;
int main()
{
T.Solve();
return 0;
}
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很久以前的奇怪但现在依旧成立的签名
attack is our red sun $$\color{red}{\boxed{\color{red}{attack\ is\ our\ red\ sun}}}$$ ------------------------------------------------------------------------------------------------------------------------
很久以前的奇怪但现在依旧成立的签名
attack is our red sun $$\color{red}{\boxed{\color{red}{attack\ is\ our\ red\ sun}}}$$ ------------------------------------------------------------------------------------------------------------------------