POJ3461 Qulipo(kmp)

传送门

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

Source

BAPC 2006 Qualification

裸字符串匹配，KMP算法

 1 #include<set>
 2 #include<queue>
 3 #include<cstdio>
 4 #include<cstdlib>
 5 #include<cstring>
 6 #include<iostream>
 7 #include<algorithm>
 8 using namespace std;
 9 const int N = 1000010;
10 #define For(i,n) for(int i=1;i<=n;i++)
11 #define Rep(i,l,r) for(int i=l;i<=r;i++)
12 char s1[N],s2[N];
13 int n,T,m,next[N];
14
15 void BuildNext(){
16     int pre=0;n=strlen(s1+1),m=strlen(s2+1);
17     Rep(i,2,n){
18         while(pre&&s1[pre+1]!=s1[i]) pre=next[pre];
19         if(s1[pre+1]==s1[i]) pre++;
20         next[i]=pre;
21     }
22 }
23
24 void KMP(){
25     int is1=0,ans=0;
26     For(is2,m){
27         while(is1&&s1[is1+1]!=s2[is2]) is1=next[is1];
28         if(s1[is1+1]==s2[is2]) is1++;
29         if(is1==n){
30             ans++;
31             is1=next[is1];
32         }
33     }
34     printf("%d\n",ans);
35 }
36
37 int main(){
38     scanf("%d",&T);
39     For(i,T){
40         scanf("%s%s",s1+1,s2+1);
41         BuildNext();
42         KMP();
43     }
44     return 0;
45 }