hdu 3086 最长回文

manacher算法的讲解：https://segmentfault.com/a/1190000008484167

#include <iostream>
#include <cstring>
#include <algorithm>
#include<stdio.h>

using namespace std;
char s[300000];
char s_new[300000];
int p[300000];

int Init()
{
    int len = strlen(s);
    s_new[0] = '$';
    s_new[1] = '#';
    int j = 2;
    for (int i = 0; i < len; i++)
    {
        s_new[j++] = s[i];
        s_new[j++] = '#';
    }
    s_new[j] = '\0';
    return j;
}

int Manacher()
{
    int len = Init();
    int max_len = -1;  
    int id = 0,mx = 0;
    for (int i = 1; i < len; i++)
    {
        p[i] = mx > i?min(p[2*id-i],mx-i):1;
        while (s_new[i - p[i]] == s_new[i + p[i]])
            p[i]++;
        if (mx < i + p[i])
        {
            id = i;
            mx = i + p[i];
        }
        max_len = max(max_len, p[i] - 1);
    }
    return max_len;
}

int main()
{
    while (scanf("%s", s)!=EOF)
    {
        printf("%d\n", Manacher());
    }
    return 0;
}