话说回文自动机我自己都还没搞懂呢……
等到时候会了再来填坑
1 //minamoto 2 #include<cstdio> 3 #include<cstring> 4 #define ll long long 5 template<class T>inline bool cmax(T&a,const T&b){return a<b?a=b,1:0;} 6 const int N=3e5+5; 7 char s[N]; 8 int n,p,q,fail[N],cnt[N],len[N],tot,last,ch[N][26]; 9 ll ans; 10 inline int newnode(int x){ 11 len[++tot]=x;return tot; 12 } 13 inline int getfail(int x,int n){ 14 while(s[n-len[x]-1]!=s[n]) x=fail[x]; 15 return x; 16 } 17 int main(){ 18 scanf("%s",s+1); 19 s[0]=-1,fail[0]=1,last=0; 20 len[0]=0,len[1]=-1,tot=2; 21 for(int i=1;s[i];++i){ 22 s[i]-='a'; 23 p=getfail(last,i); 24 if(!ch[p][s[i]]){ 25 q=newnode(len[p]+2); 26 fail[q]=ch[getfail(fail[p],i)][s[i]]; 27 ch[p][s[i]]=q; 28 } 29 ++cnt[last=ch[p][s[i]]]; 30 } 31 for(int i=tot;i;--i) 32 cnt[fail[i]]+=cnt[i],cmax(ans,1ll*cnt[i]*len[i]); 33 printf("%lld ",ans); 34 return 0; 35 }