POJ 3974 Palindrome（最长回文子串）

题目链接：http://poj.org/problem?id=3974

题意：求一给定字符串最长回文子串的长度

思路：直接套模板manacher算法

code：

 1 #include <cstdio>

 2 #include <cstring>

 3 #include <algorithm>

 4 using namespace std;

 5 const int MAXN = 1000010;

 6 char Ma[2*MAXN];

 7 int Mp[2*MAXN];

 8 

 9 void Manacher(char s[], int len)

10 {

11     int l = 0;

12     Ma[l++] = 'S';

13     Ma[l++] = '#';

14     for (int i = 0; i < len; ++i)

15     {

16         Ma[l++] = s[i];

17         Ma[l++] = '#';

18     }

19     Ma[l] = 0;

20     int mx = 0;

21     int id = 0;

22     for (int i = 0; i < l; ++i)

23     {

24         Mp[i] = mx > i ? min(Mp[2*id-i], mx-i) : 1;

25         while (Ma[i+Mp[i]] == Ma[i-Mp[i]]) ++Mp[i];

26         if (i + Mp[i] > mx)

27         {

28             mx = i +Mp[i];

29             id = i;

30         }

31     }

32 }

33 

34 char s[MAXN];

35 

36 int main()

37 {

38     int cnt = 0;

39     while (scanf("%s", s) != EOF)

40     {

41         if (strcmp(s, "END") == 0) break;

42         int len = strlen(s);

43         Manacher(s, len);

44         int ans = 0;

45         len = 2 * len + 2;

46         for (int i = 0; i < len; ++i) ans = max(ans, Mp[i] - 1);

47         printf("Case %d: %d\n",++cnt, ans);

48     }

49     return 0;

50 }