hdu 3068 最长回文 Manacher算法模板题

#include <iostream>
#include <cstdio>
#include <algorithm>
using namespace std;
const int N = 200010;
char s
, str[N*2];
int p[N*2];
int manacher()
{
int i;
for(i = 1; s[i]; i++)
str[i*2] = s[i], str[i*2+1] = '#';
str[0] = '?', str[1] = '#', str[i*2] = '\0';
int res = 0, k = 0, maxk = 0;
for(int i = 2; str[i]; i++)
{
p[i] = i < maxk ? min(maxk - i, p[2*k-i]) : 1;
while(str[i-p[i]] == str[i+p[i]]) p[i]++;
if(p[i] + i > maxk)
k = i, maxk = i + p[i];
res = max(res, p[i]);
}
return res - 1;
}
int main()
{
while(~scanf("%s",s+1))
cout<<manacher()<<endl;
return 0;
}