[hdu 3068] Manacher算法O(n)最长回文子串

一个不错的讲解：https://github.com/julycoding/The-Art-Of-Programming-By-July/blob/master/ebook/zh/01.05.md

#include<bits/stdc++.h>
using namespace std;

const int MAXN=110010;
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;
        }
    }
}
/*
* abaaba
* i: 0 1 2 3 4 5 6 7 8 9 10 11 12 13
* Ma[i]: $ # a # b # a # a $ b # a #
* Mp[i]: 1 1 2 1 4 1 2 7 2 1 4 1 2 1
*/
char s[MAXN];
int main()
{
    while(scanf("%s",s)==1)
    {
        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;
}