字符串算法专题

ACM中常用的字符串算法不多,主要有以下几种:

1. Hash
2. 字典树
3. KMP
4. AC自动机
5. manacher
6. 后缀数组
7. EX_KMP
8. SAM(后缀自动机)
9. 回文串自动机

一. Hash

hash常用算法：

 1 #define M 249997
 2 /*APHash*/
 3 unsigned int APHash(String str)
 4 {
 5     unsigned int hash = 0xAAAAAAAA;
 6     for(int i = 0; i < str.length(); i++)
 7     {
 8         if((i & 1) == 0)
 9         hash ^=((hash << 7) ^ str.charAt(i) ^ (hash >> 3));
10         else
11         hash ^= (~((hash << 11) ^ str.charAt(i) ^ (hash >> 5)));
12     }
13     return (hash%M);
14 }
15 //RSHash
16 unsigned int RSHash(String str)
17 {
18     unsigned int b = 378551;
19     unsigned int a = 63689;
20     unsigned int hash = 0;
21     for(int i = 0; i < str.length(); i++)
22     {
23         hash = hash * a + str.charAt(i);//这里可能需要改成srt.At(i) 
24         a = a * b;
25      }
26      return (hash%M);
27  }
28 /*DJBHash*/
29 unsigned int DJBHash(String str)
30 {
31     unsigned int hash = 5381;
32     for(int i = 0; i < str.length(); i++)
33     hash = ((hash << 5) + hash) + str.charAt(i);
34     return (hash%M);
35  }
36 /*JSHash*/
37 unsigned int JSHash(String str)
38 {
39     unsigned int hash = 1315423911;
40     for(int i = 0; i < str.length(); i++)
41     hash ^= ((hash << 5) + str.charAt(i) + (hash >> 2));
42     return (hash%M);
43 }
44 /*SDBMHash*/
45 unsigned int SDBMHash(String str)
46 {
47     unsigned int hash = 0;
48     for(int i = 0; i < str.length(); i++)
49     hash = str.charAt(i) + (hash << 6) + (hash << 16) - hash;
50     return (hash%M);
51 }
52 /*PJWHash*/
53 unsigned int PJWHash(String str)
54 {
55     unsigned int BitsInUnsignedInt = (unsigned int)(sizeof(unsigned int)*8);
56     (unsigned int) ThreeQuarters = (unsigned int)((BitsInUnsignedInt * 3) / 4);
57     (unsigned int) OneEighth = (unsigned int)(BitsInUnsignedInt / 8);
58     (unsigned int) HighBits = (unsigned int)(0xFFFFFFFF)<<(BitsInUnsignedInt-OneEighth);
59     (unsigned int) hash = 0;
60     (unsigned int) test = 0;
61     for(int i = 0; i < str.length(); i++)
62      {
63       hash = (hash << OneEighth) + str.charAt(i);
64       if((test = hash & HighBits) != 0)
65       hash = ((hash ^ (test >> ThreeQuarters)) & (~HighBits));
66       }
67      return (hash%M);
68 }
69 }

hash常用经典字符串算法

1 unsigned int BKDRHash(char*str)
2 {
3     unsigned int seed=131;
4     unsigned int hash=0 ;
5     for(int i = 0; i < str.length(); i++)
6     hash = (hash * seed) + str.charAt(i);
7     return(hash % M);
8 }

 对于hash的理解可以见我另一份博客随笔，在算法专题栏中。