HDU 3068 回文串--Manacher

//2009 Multi-University Training Contest 16 - Host by NIT

//最长回文

#include <cstdio>

#include <cstring>

#include <algorithm>



using namespace std;



const int maxn = 100000 + 10;



char Ma[maxn*2];

int Mp[maxn*2];



void Manacher(char s[],int len)

{

	int l=0;

	Ma[l++]='$';

	Ma[l++]='#';

	for(int i=0;i<len;i++)

	{

		Ma[l++]=s[i];

		Ma[l++]='#';

	}

	Ma[l]=0;

	int mx=0,id=0;

	for(int i=0;i<l;i++)

	{

		Mp[i]=mx>i?min(Mp[2*id-i],mx-i):1;

		while(Ma[i+Mp[i]]==Ma[i-Mp[i]]) Mp[i]++;

		if(i+Mp[i]>mx)

		{

			mx=i+Mp[i];

			id=i;

		}

	}

}



char s[maxn];



int main()

{

	while(~scanf("%s",s))

	{

		int len=strlen(s);

		Manacher(s,len);

		int ans=0;

		for(int i=0;i<2*len+2;i++)

			ans=max(ans,Mp[i]-1);

		printf("%d\n",ans);

	}

	return 0;

}