[bzoj3676][APIO2014]回文串

题目大意

求出所有回文串在S中出现次数乘长度的最大值。

裸题

直接回文自动机跑啊！

#include<cstdio>
#include<cstring>
#include<algorithm>
#define fo(i,a,b) for(i=a;i<=b;i++)
#define fd(i,a,b) for(i=a;i>=b;i--)
using namespace std;
typedef long long ll;
const ll maxn=300000+10;
ll pre[maxn],len[maxn],size[maxn],g[maxn][26];
ll i,j,k,l,t,n,m,ans,tot,last;
char s[maxn];
void insert(char ch){
 ll x=last;
 while (s[i-len[x]-1]!=s[i]) x=pre[x];
 if (!g[x][ch-'a']){
 len[++tot]=len[x]+2;
 ll y=pre[x];
 while (s[i-len[y]-1]!=s[i]) y=pre[y];
 pre[tot]=g[y][ch-'a'];
 g[x][ch-'a']=tot;
 }
 x=g[x][ch-'a'];
 size[x]++;
 last=x;
}
int main(){
 freopen("palindrome.in","r",stdin);freopen("palindrome.out","w",stdout);
 scanf("%s",s+1);
 n=strlen(s+1);
 len[pre[last=0]=tot=1]=-1;
 pre[1]=1;
 fo(i,1,n) insert(s[i]);
 fd(i,tot,2) 
 if (pre[i]>1) size[pre[i]]+=size[i];
 fo(i,2,tot) ans=max(ans,len[i]*size[i]);
 printf("%lld\n",ans);
}