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 }

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