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.

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.

 

 1 #include<stdio.h>
 2 #include<string.h>
 3 
 4 const int MAXN = 1e6+1;
 5 
 6 char Mum[MAXN], Son[10001];
 7 int next[MAXN];
 8 int count;
 9 void GetNext(int l2)
10 {
11 int i = 0, j = -1;
12 next[0] = -1;
13 while(i < l2)
14 {
15 if(j == -1 || Son[i]==Son[j])
16 next[++i] = ++j;
17 else
18 j = next[j];
19 }
20 }
21 void KMP(int l1, int l2)
22 {
23 int i=0, j=0;
24 GetNext(l2);
25 while(i < l1)
26 {
27 if(j==-1 || (Mum[i]==Son[j]&&i<l1&&j<l2) )
28 i++, j++;
29 else
30 j = next[j];
31 if(j == l2)
32 {
33 count++;
34 j = next[j];
35 }
36 }
37 }
38 
39 int main()
40 {
41 int T;
42 
43 scanf("%d", &T);
44 
45 while(T--)
46 {
47 int Mn, Sn;
48 scanf("%s", Son);
49 scanf(" %s", Mum);
50 Sn = strlen(Son);
51 Mn = strlen(Mum);
52 count = 0;
53 KMP(Mn, Sn);
54 printf("%d\n", count);
55 }
56 return 0;
57 }