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.

InputThe 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.
OutputFor 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

http://blog.csdn.net/v_july_v/article/details/7041827（kmp的算法详解）

 1 #include<iostream>
 2 #include<cstring>
 3 #include<string>
 4 #include<cstdio>
 5 using namespace std;
 6 
 7 int n;
 8 int nxt[1000005];
 9 char p[10005],s[1000005];
10 
11 void getNext(char *p){
12     nxt[0]=-1;
13     int len=strlen(p);
14     for(int i=0;i<len;i++){
15         int k=nxt[i];
16         while(k!=-1&&p[i]!=p[k]) k=nxt[k];
17         nxt[i+1]=k+1;
18     }
19 }
20 
21 int kmp(char *s,char *p){
22     getNext(p);
23     int ans=0,i=0,j=0,lens=strlen(s),lenp=strlen(p);
24     while(i<lens){
25         if(j==-1||s[i]==p[j]){
26             i++;
27             j++; 
28         }
29         else j=nxt[j];
30         if(j==lenp){
31             ans++;
32             j=nxt[j];
33         }
34     }
35     return ans;
36 }
37 
38 int main()
39 {   scanf("%d",&n);
40     while(n--){
41         scanf("%s%s",p,s);
42         printf("%d\n",kmp(s,p));
43     }
44 }

Oulipo HDU - 1686