@[endswitch](/user/773915)
$p_i$ 中间那里应该要判断边界吧
by _JF_ @ 2024-02-05 21:12:47
@[_JF_](/user/361141) 您可以具体说一说吗
by endswitch @ 2024-02-05 21:13:36
@[endswitch](/user/773915)
```cpp
while(a[i-p[i]]==a[i+p[i]]) p[i]++;
```
应该要判断是否越过 $1$ 和 $n$吧
by _JF_ @ 2024-02-05 21:15:46
@[_JF_](/user/361141) 理论上应该不需要吧（我的边界赋初值了）
by endswitch @ 2024-02-05 21:18:44
@[endswitch](/user/773915)
```cpp
#include <bits/stdc++.h>
using namespace std;
const int N=2.2e7+5;
int j,l,mid,ans,p[N];
char a[N],s[N];
signed main() {
ios_base::sync_with_stdio(NULL);
cin.tie(nullptr);
cout.tie(nullptr);
cin>>(s+1);
l=strlen(s+1);
for(int i=1;i<=l;i++)
a[(i<<1)-1]=s[i],a[i<<1]='*';
l=strlen(a+1),a[0]='/';
for(int i=1;i<=l;i++) {
if(i<=j) p[i]=min(p[(mid<<1)-i],j-i+1);
while(a[i-p[i]]==a[i+p[i]]) p[i]++;
if(p[i]+i>j) j=p[i]+i-1,mid=i;
}
for(int i=1;i<=l;i++)
ans=max(ans,p[i]-1);
cout<<ans;
return 0;
}
```
84
by 2011FYCCCTA @ 2024-02-05 21:20:16
@[2011FYCCCTA](/user/923403) 这个我是试过的了，，
而且我不改就是对的这份做法错误的点
by endswitch @ 2024-02-05 21:21:48
欸我好像标题写错了（
应该是 16 pts 才对（
by endswitch @ 2024-02-05 21:22:23
@[endswitch](/user/773915) 哦
by 2011FYCCCTA @ 2024-02-05 21:22:54