HDU 3068 最长回文

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 const int maxn = 200010;
 4 struct PalindromicTree{
 5     int son[maxn][26],fail[maxn],len[maxn],s[maxn];
 6     int tot,last,n,maxlen;
 7     int newnode(int slen = 0){
 8         len[tot] = slen;
 9         memset(son[tot],0,sizeof son[tot]);
10         return tot++;
11     }
12     void init(){
13         maxlen = tot = last = n = 0;
14         newnode(0);
15         newnode(-1);
16         fail[0] = fail[1] = 1;
17         s[n] = -1;
18     }
19     int getFail(int x){
20         while(s[n - len[x] -1] != s[n]) x = fail[x];
21         return x;
22     }
23     void extend(int c){
24         s[++n] = c;
25         int cur = getFail(last);
26         if(!son[cur][c]){
27             int x = newnode(len[cur] + 2);
28             fail[x] = son[getFail(fail[cur])][c];
29             son[cur][c] = x;
30             maxlen = max(maxlen,len[x]);
31         }
32         last = son[cur][c];
33     }
34 }pt;
35 char str[maxn];
36 int main(){
37     while(~scanf("%s",str)){
38         pt.init();
39         for(int i = 0; str[i]; ++i)
40             pt.extend(str[i] - ‘a‘);
41         printf("%d\n",pt.maxlen);
42     }
43     return 0;
44 }