KMP模式匹配算法:Oulipo

Description

The French author Georges Perec (1936–1982) once wrote a book, La disparition, without the letter 'e'. He was a member of the Oulipo group. A quote from the book:

Tout avait Pair normal, mais tout s’affirmait faux. Tout avait Fair normal, d’abord, puis surgissait l’inhumain, l’affolant. Il aurait voulu savoir où s’articulait l’association qui l’unissait au roman : stir son tapis, assaillant à tout instant son imagination, l’intuition d’un tabou, la vision d’un mal obscur, d’un quoi vacant, d’un non-dit : la vision, l’avision d’un oubli commandant tout, où s’abolissait la raison : tout avait l’air normal mais…

Perec would probably have scored high (or rather, low) in the following contest. People are asked to write a perhaps even meaningful text on some subject with as few occurrences of a given “word” as possible. Our task is to provide the jury with a program that counts these occurrences, in order to obtain a ranking of the competitors. These competitors often write very long texts with nonsense meaning; a sequence of 500,000 consecutive 'T's is not unusual. And they never use spaces.

So we want to quickly find out how often a word, i.e., a given string, occurs in a text. More formally: given the alphabet {'A', 'B', 'C', …, 'Z'} and two finite strings over that alphabet, a word W and a text T, count the number of occurrences of W in T. All the consecutive characters of W must exactly match consecutive characters of T. Occurrences may overlap.

Input

The first line of the input file contains a single number: the number of test cases to follow. Each test case has the following format:

• One line with the word W, a string over {'A', 'B', 'C', …, 'Z'}, with 1 ≤ |W| ≤ 10,000 (here |W| denotes the length of the string W).
• One line with the text T, a string over {'A', 'B', 'C', …, 'Z'}, with |W| ≤ |T| ≤ 1,000,000.

Output

For every test case in the input file, the output should contain a single number, on a single line: the number of occurrences of the word W in the text T.

Sample Input

3

BAPC

BAPC

AZA

AZAZAZA

VERDI

AVERDXIVYERDIAN

Sample Output

1

3

0

 1 #include <cstdio>

 2 #include <iostream>

 3 #include <cstring>

 4 #include <string>

 5 

 6 using namespace std;

 7 

 8 const int MAX = 1000010;

 9 

10 int next[MAX], slen, tlen;

11 char s[MAX], t[MAX];

12 

13 void get_next();

14 int kmp();

15 

16 int main()

17 {

18 #ifdef OFFLINE

19     freopen("in.txt","r",stdin);

20     freopen("out.txt","w",stdout);

21 #endif

22 

23     int n;

24     scanf("%d",&n);

25     while(n--)

26     {

27         slen = tlen = 0;

28         memset(next, 0, sizeof(next));

29         memset(s, 0, sizeof(s));

30         memset(t, 0, sizeof(t));

31 

32         scanf("%s%s", &t, &s);

33         slen = strlen(s);

34         tlen = strlen(t);

35 

36         printf("%d\n",kmp());

37     }

38     return 0;

39 }

40 

41 void get_next()

42 {

43     int i = 0, j = -1;

44     next[0] = -1;

45     while(i < tlen)

46     {

47         if(j == -1 || t[i] == t[j])

48             next[++i] = ++j;

49         else

50             j = next[j];

51     }

52 }

53 

54 int kmp()

55 {

56     int ans = 0;

57     int i, j = 0;

58     if (tlen == 1 && slen == 1)

59     {

60         if (t[0] == s[0])

61             return 1;

62         else

63             return 0;

64     }

65 

66     get_next();

67 

68     for (i = 0;i < slen; i++)

69     {

70         while (j > 0 && s[i] != t[j]) j = next[j];

71         if (t[j] == s[i]) j++;

72         if (j == tlen)

73         {

74             ans++;

75             j = next[j];

76         }

77     }

78 

79     return ans;

80 }

View Code