bzoj2565 最长双回文串

 1 //It is made by wfj_2048~
 2 #include <algorithm>
 3 #include <iostream>
 4 #include <complex>
 5 #include <cstring>
 6 #include <cstdlib>
 7 #include <cstdio>
 8 #include <vector>
 9 #include <cmath>
10 #include <queue>
11 #include <stack>
12 #include <map>
13 #include <set>
14 #define inf (1<<30)
15 #define N (200010)
16 #define il inline
17 #define RG register
18 #define ll long long
19 #define File(s) freopen(s".in","r",stdin),freopen(s".out","w",stdout)
20 
21 using namespace std;
22 
23 int ans;
24 
25 struct PAM{
26 
27     int ch[N][26],fa[N],l[N],len[N],n,la,sz;
28     char s[N];
29 
30     il void pre(){ l[++sz]=-1,fa[0]=1; return; }
31 
32     il void add(RG int c,RG int n){
33     RG int x=la; while (s[n-l[x]-1]!=s[n]) x=fa[x];
34     if (!ch[x][c]){
35         RG int v=++sz,k=fa[x]; l[v]=l[x]+2;
36         while (s[n-l[k]-1]!=s[n]) k=fa[k];
37         fa[v]=ch[k][c],ch[x][c]=v;
38     }
39     la=ch[x][c],len[n]=l[ch[x][c]]; return;
40     }
41     
42 }tr1,tr2;
43 
44 il void work(){
45     scanf("%s",tr1.s+1),tr1.n=strlen(tr1.s+1),tr2.n=tr1.n,tr1.pre();
46     for (RG int i=1;i<=tr2.n;++i) tr2.s[i]=tr1.s[tr1.n-i+1]; tr2.pre();
47     for (RG int i=1;i<=tr1.n;++i)
48     tr1.add(tr1.s[i]-97,i);
49     for (RG int i=1;i<=tr2.n;++i) tr2.add(tr2.s[i]-97,i);
50     for (RG int i=1;i<tr1.n;++i) ans=max(ans,tr1.len[i]+tr2.len[tr2.n-i]);
51     printf("%d\n",ans); return;
52 }
53 
54 int main(){
55     File("PAM");
56     work();
57     return 0;
58 }