1 #include<bits/stdc++.h>
 2 using namespace std;
 3 const int MAX=21000020;
 4 char s[MAX],t[MAX<<1];
 5 int p[MAX<<1],cnt=0,mid,mr;
 6 void manachar()
 7 {
 8     t[cnt++]=‘$‘;
 9     int len=strlen(s);
10     for(int i=0;i<len;i++)
11     {
12         t[cnt++]=‘#‘;
13         t[cnt++]=s[i];
14     }
15     t[cnt++]=‘#‘;
16     t[cnt]=‘\0‘;
17     
18     for(int i=0;i<cnt;i++)
19     {
20         p[i]=i<mr?min(p[(mid<<1)-i],mr-i):1;
21         for(;t[p[i]+i]==t[i-p[i]] and p[i]+i<cnt;p[i]++)
22             if(p[i]+i>mr)
23             {
24                 mid=i;
25                 mr=p[i]+i;
26             }
27     }
28 }
29 int main()
30 {
31     scanf("%s",s);
32     manachar();
33     int ans=1;
34     for(int i=0;i<cnt;i++)
35         ans=max(ans,p[i]);
36     printf("%d",ans-1);
37     return 0;
38 }

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 const int MAX=1e5+10;
 4 char pic[MAX],s1[MAX<<1],s2[MAX<<1];
 5 int p1[MAX<<1],p2[MAX<<1],cnt=2;
 6 int ans1[MAX<<1] ,ans2[MAX<<1],len;
 7 void manachar(char * s,int * p,int * ans)
 8 {
 9     int mid=0,mr=0;
10     for(int i=0;i<cnt;i++)
11     {
12         p[i]=i<mr?min(p[mid*2-i],mr-i):1;
13         for(;s[p[i]+i]==s[i-p[i]];p[i]++)
14             if(i+p[i]>mr)
15             {
16                 mr=i+p[i];
17                 ans[mr]=p[i];
18                 mid=i;
19             }
20     }
21 }
22 int main()
23 {
24     scanf("%s",pic);
25     len=strlen(pic);
26     s1[0]=s2[0]=‘$‘;
27     s1[1]=s2[1]=‘#‘;
28     for(int i=0;i<len;i++)
29     {
30         s1[cnt]=pic[i];
31         s2[cnt]=pic[len-i-1];
32         s1[++cnt]=‘#‘;
33         s2[cnt++]=‘#‘;
34     }
35     cnt++;
36     s1[cnt]=s2[cnt]=‘\0‘;
37     manachar(s1,p1,ans1);
38     manachar(s2,p2,ans2);
39     int j=cnt-4,ans=2;
40     for(int i=3;i<cnt-2;i++)
41     {
42         if(s1[i]==‘#‘)
43             ans=max(ans,ans1[i]+ans2[j]);
44         j--;
45     }
46     cout<<ans<<endl;
47     return 0;
48 }