HDU3068最长回文 题解

#include<cstdio>
#include<cstring>
#include<iostream>
#define M 350000
using namespace std;

int r[M];
char s[M],str[M];

int main()
{
    while (scanf("%s",s)!=EOF)
    {
        int i,k,l=strlen(s),ans=0,maxr=0;
        for (str[0]=‘$‘,i=l;i>=0;i--) str[i+i+2]=s[i],str[i+i+1]=‘#‘;
        for (i=2;i<=l+l;i++)
        {
            r[i]=maxr>i?min(r[k+k-i],maxr-i):1;
            for (;str[i-r[i]]==str[i+r[i]];r[i]++);
            if (i+r[i]>maxr) maxr=i+r[i],k=i;
            ans=max(r[i],ans);
        }
        printf("%d\n",ans-1);
    }
    return 0;
}