bzoj2565 最长双回文串

#include<cstdio>
#define N 100005
char s[N<<1];
int p[N<<1],a[N<<1];
int len,mx,pos,ans;
inline int max(const int &a,const int &b){return a>b?a:b;}
inline int min(const int &a,const int &b){return a<b?a:b;}
inline void getstring()
{
char c=getchar();
while(c<'a'||c>'z') c=getchar();
while(c>='a'&&c<='z') s[++len]='#',s[++len]=c,c=getchar();
s[0]='$',s[len+1]=s[len+2]='#';
}
int main()
{
getstring();
for(int i=1;i<=len;i++)
{
if(mx>i) p[i]=min(p[pos*2-i],mx-i);
else p[i]=1;
if(!a[i+p[i]]) a[i+p[i]]=i;
ans=max(ans,i-a[i-p[i]]);
while(s[i+p[i]]==s[i-p[i]])
{
if(!a[i+p[i]]) a[i+p[i]]=i;
ans=max(ans,i-a[i-p[i]]);
p[i]++;
}
if(i+p[i]>mx) mx=i+p[i],pos=i;
}
printf("%d",ans);
return 0;
}