HDU-3068-最长回文 (Manacher算法)

aaaa

abab

4
3

思路：这里讲得非常具体了http://blog.csdn.net/ggggiqnypgjg/article/details/6645824

#include <cstdio>
using namespace std;

char s[110005],str[220010];
int p[220010];

int main()
{
    int len,i,maxlen,maxindex,ans;

    while(~scanf("%s",s))
    {
        str[0]=‘$‘;
        str[1]=‘#‘;

        for(i=0;s[i];i++)
        {
            str[i*2+2]=s[i];
            str[i*2+3]=‘#‘;
        }

        len=i*2+2;
        str[len]=‘\0‘;

        maxlen=0;
        for(i=1;i<len;i++)
        {
            if(maxlen>i) p[i]=p[2*maxindex-i]<maxlen-i?p[2*maxindex-i]:maxlen-i;
            else p[i]=1;

            while(str[i-p[i]]==str[i+p[i]])
            {
                p[i]++;
            }

            if(p[i]+i>maxlen)
            {
                maxlen=p[i]+i;
                maxindex=i;
            }
        }

        ans=0;
            
        for(i=1;i<len;i++) if(ans<p[i]) ans=p[i];

        printf("%d\n",ans-1);
    }
}