Hdu 3294 Girls' research (manacher 最长回文串)

题目链接：

　　Hdu 3294  Girls‘ research

题目描述：

　　给出一串字符串代表暗码，暗码字符是通过明码循环移位得到的，比如给定b，就有b == a，c == b,d == c,.......,a == z。

问最长回文串所在区间，以及最长回文串所表示的明码。

解题思路：

　　字符串长度[1,200000]，用manacher算法很轻松就搞定了。

　　get√新技能请点击me

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <iostream>
 4 #include <algorithm>
 5 using namespace std;
 6 const int maxn = 400005;
 7 char str[maxn];
 8 int p[maxn];
 9 int main ()
10 {
11     int x, maxlen;
12     char s[2];
13     while (scanf ("%s %s", s, str) != EOF)
14     {
15         memset (p, 0, sizeof(p));
16         int len = strlen (str);
17         for (int i=len; i>=0; i--)
18         {
19             str[i*2+2] = str[i];
20             str[i*2+1] = ‘#‘;
21         }
22         str[0] = ‘*‘;//str两端标志为不同字符，防止下标越界
23         x = maxlen = 0;
24         len = len * 2 + 1;
25         for (int i=2; i<len; i++)
26         {
27             if (p[x]+x > i)
28                 p[i] = min (p[2*x-i], p[x]-i+x);
29             else
30                 p[i] = 1;
31             while (str[i-p[i]] == str[i+p[i]])
32                 p[i] ++;
33             if (x+p[x] < i+p[i])
34                 x = i;
35             if (maxlen < p[i])
36                 maxlen = p[i];
37         }//manacher模板
38         if (maxlen <= 2)
39         {
40             printf ("No solution!\n");
41             continue;
42         }
43         int res = s[0] - ‘a‘, a, b;
44         for (int i=2; i<len; i++)
45             if (p[i] == maxlen)
46             {
47                 //找到回文串所在区间
48                 a = i - p[i] + 2;
49                 b = i + p[i] - 2;
50                 break;
51             }
52         printf ("%d %d\n", a/2-1, b/2-1);
53         for (int i=a; i<=b; i+=2)
54         {
55             str[i] -= res;
56             if (str[i] < ‘a‘)
57                 str[i] += 26;
58             putchar(str[i]);
59         }
60         printf("\n");
61     }
62     return 0;
63 }

Hdu 3294 Girls' research (manacher 最长回文串)