边吃边敲，效率就是高

代码如下：

#include<stdio.h>
#include<string.h>
#define MAX  1000050
char s[MAX],ss[MAX*2];
int  p[MAX*2];
int min(int a,int b){return a>b?b:a;}
int main()
{
  int i,id,mx,max,n,j;
  j=1;
  
  while(scanf("%s",s)!=EOF,s[0]!='E')
  {
    ss[0]='$';
    n=strlen(s);
    for(i=0;i<n;i++)
    {
      ss[2*i+1]='#';
      ss[2*(i+1)]=s[i];
    }
    ss[2*i+1]='#';
    ss[2*(i+1)]='\0';
    id=1;
    max=0;
    mx=0;
    for(i=1;i<2*n+2;i++)
    {
      if(mx>i)
      p[i]=min(p[2*id-i],mx-i);
      else
      p[i]=1;
      while(ss[i+p[i]]==ss[i-p[i]])
      {
        p[i]++;
      }
      if(i+p[i]>mx) 
      {
          mx=i+p[i];
          id=i;
      }
      if(p[i]>max)  max=p[i];
      
    }
    printf("Case %d: %d\n",j++,max-1);
  }
  return 0;
}

poj 3974 Palindrome