manacher（马拉车）求最长回文子串长度

#include<cstdio>
#include<cstring>
#include<iostream>
using namespace std;
char str[100000];
char s[200000];
int r[200000];
int main()
{
	memset(s,0,sizeof(s));
	memset(r,0,sizeof(r));
	scanf("%s",str);
	int len=strlen(str);
	int i;
	for(i=0;i<len;i++)
	{
		s[i*2]='#';
		s[i*2+1]=str[i];
	}
	s[i*2]='#';
	s[i*2+1]='\0';
	len=strlen(s);
	int maxright=0;
	int pos=0;
	int ans=0;
	for(int i=1;i<len;i++)
	{
		if(i<maxright)
		r[i]=min(maxright-i,r[2*pos-i]);
		else
		r[i]=1;
		while(s[i-r[i]]==s[i+r[i]]&&i-r[i]>=0)
		r[i]++;
		if(i+r[i]-1>maxright)
		{
			maxright=i+r[i]-1;
			pos=i;
		}
		ans=max(ans,r[i]);
	}
	printf("%d",ans-1);
	return 0;	
}