HDU ~ 3068 ~ 最长回文 （Manacher模板题）

思路：Manacher算法。 用string输入输出会超时。

算法讲解大家可以看这篇博客：Manacher算法--O（n）回文子串算法

#include<bits/stdc++.h>
using namespace std;
const int MAXN = 110005 * 2;
//int Manacher(string a)
int Manacher(char a[])
{
    int len = strlen(a)/*a.size()*/, id = 0, MAX = 0, ans = -1, p[MAXN];
    memset(p, 0, sizeof(p));
    //string s = "$#";
    char s[MAXN] = "$#";
    //for (int i = 0; i < len; i++){ s += a[i]; s += '#'; }
    for (int i = 0; i < len; i++){ s[i * 2 + 2] = a[i]; s[i * 2 + 3] = '#'; }
    len = len * 2 + 1;
    for (int i = 1; i <= len; i++)
    {
        if (MAX > i) p[i] = min(p[2 * id - i], MAX - i);
        else p[i] = 1;
        while(s[i - p[i]] == s[i + p[i]]) p[i]++;
        ans = max(ans, p[i]);
        if(MAX < p[i] + i)
        {
            MAX = p[i] + i;
            id = i;
        }
    }
    return ans - 1;
}
int main()
{
    //string s;
    char s[MAXN];
    //while (cin >> s)
    while (~scanf("%s", s))
    {
        printf("%d\n", Manacher(s));
    }
    return 0;
}
/*
aaaa

abab
*/