Manacher

 1 #include <cstdio>
 2 #include <cstring>
 3 const int Maxn=110100;
 4 char Str[Maxn<<1],STR[Maxn<<1];
 5 int Len,x,P[Maxn<<1],Id,Mx;
 6 inline int Max(int x,int y) {return x>y?x:y;}
 7 inline int Min(int x,int y) {return x>y?y:x;}
 8 inline Init()
 9 {
10     Len=strlen(Str+1);
11     for (int i=1;i<=Len;i++) STR[i]=Str[i];
12     Str[0]=‘$‘; Str[1]=‘#‘;
13     for (int i=1;i<=Len;i++) Str[i<<1]=STR[i],Str[i<<1|1]=‘#‘;
14     Len=Len<<1|1; Id=1;Mx=0;
15 }
16 inline int Manacher()
17 {
18     for (int i=2;i<=Len;i++)
19     {
20         if (Mx>i) P[i]=Min(P[2*Id-i],Mx-i); else P[i]=1;
21         while (Str[i+P[i]]==Str[i-P[i]]) P[i]++;
22         if (i+P[i]>Mx) Mx=P[i]+i,Id=i;
23     }
24     int Ret=0;
25     for (int i=1;i<=Len;i++)  Ret=Max(Ret,P[i]);
26     return Ret-1;
27 }
28 int main()
29 {
30     while (scanf("%s",Str+1)!=EOF)
31     {
32         Init();
33         printf("%d\n",Manacher());
34     }
35     return 0;
36 }