回文树详解

 1 #include<iostream>
 2 #include<cstring>
 3 #include<cstdio>
 4 //#include<time.h>
 5 //#include<complex>
 6 //#include<set>
 7 //#include<queue>
 8 #include<algorithm>
 9 #include<stdlib.h>
10 using namespace std;
11 
12 #define LL long long
13 int qread()
14 {
15     char c; int s=0,f=1; while ((c=getchar())<‘0‘ || c>‘9‘) (c==‘-‘) && (f=-1);
16     do s=s*10+c-‘0‘; while ((c=getchar())>=‘0‘ && c<=‘9‘); return s*f;
17 }
18 
19 //Pay attention to ‘-‘ , LL and double of qread!!!!
20 
21 int n,m;
22 #define maxn 1000011
23 char s[maxn];
24 struct PT
25 {
26     struct Node{int ch[26],len,pre,cnt;}a[maxn];
27     int last,size;
28     PT() {size=2; last=2; a[1].len=-1; a[2].len=0; a[2].pre=a[1].pre=1;}
29     void insert(int c,int p)
30     {
31         int y=last,len=0;
32         while (1)
33         {
34             len=a[y].len;
35             if (p-len-1>=0 && s[p-len-1]==s[p]) break;
36             y=a[y].pre;
37         }
38         if (a[y].ch[c]) {last=a[y].ch[c]; a[last].cnt++; return;}
39         int x=last=++size;
40         a[x].len=a[y].len+2; a[y].ch[c]=x; a[x].cnt=1;
41         if (a[x].len==1) {a[x].pre=2; return;}
42         while (1)
43         {
44             y=a[y].pre;
45             len=a[y].len;
46             if (p-1-len>=0 && s[p-len-1]==s[p])
47             {
48                 a[x].pre=a[y].ch[c];
49                 break;
50             }
51         }
52     }
53     void hei()
54     {
55         for (int i=size;i;i--) a[a[i].pre].cnt+=a[i].cnt;
56     }
57     void test()
58     {
59         for (int i=1;i<=size;i++) cout<<a[i].len<<‘ ‘<<a[i].pre<<endl;
60     }
61 }pt;
62 
63 int main()
64 {
65     scanf("%s",s+1); n=strlen(s+1);
66     for (int i=1;i<=n;i++) pt.insert(s[i]-‘a‘,i);
67     pt.hei();
68     int ans=0;
69     for (int i=3;i<=pt.size;i++) ans+=pt.a[i].cnt;
70     printf("%d\n",ans);
71     return 0;
72 }