最长回文子串之Manacher算法【模板】

模板

#include<iostream>
#include<string>
#include<cstring>

using namespace std;

const int N=100000;
int p[2*N+10];

int Manacher(string s)
{
	if(s=="")
	  return 0;
	int mx=0,id=0,len=s.length();
	memset(p,0,sizeof(p));
	for(int k=0;k<=len*2+1;k+=2)
	  s.insert(k,"#");
	for(int i=0;s[i];i++){
		p[i]=mx>i?min(p[2*id-i],mx-i):1;
		while((i+p[i]<s.length())&&(i-p[i]>=0)&&s[i+p[i]]==s[i-p[i]])
		  p[i]++;
		if(i+p[i]>mx){
			mx=i+p[i];
			id=i;
		}
	}
	int ans=1;
	for(int i=0;i<s.length();i++)
	  if(ans<p[i])
	    ans=p[i];
	return ans-1;
}

int main()
{
	string s;
	cin>>s;
	cout<<Manacher(s)<<endl;
	return 0;
}