kuangbin专题十六 KMP&&扩展KMP HDU1686 Oulipo

Posted 2021-02-03 acmerszl

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



在主串中匹配到j>=plen时，j继续回溯。

 1 #include<stdio.h>
 2 #include<string.h>
 3 int Next[10010],n,m,_,tlen,plen;
 4 char t[1000010],p[10010];
 5 
 6 void prekmp() {
 7     tlen=strlen(t);
 8     plen=strlen(p);
 9     int i,j;
10     j=Next[0]=-1;
11     i=0;
12     while(i<plen) {
13         while(j!=-1&&p[i]!=p[j]) j=Next[j];
14         if(p[++i]==p[++j]) Next[i]=Next[j]; //这里判断的是模式串
15         else Next[i]=j;
16     }
17 }
18 
19 int kmp() {
20     prekmp();
21     int i,j,ans=0;
22     i=j=0;
23     while(i<tlen) {
24         while(j!=-1&&t[i]!=p[j]) j=Next[j];
25         i++;j++;
26         if(j>=plen) {  //主要区别
27             ans++;
28             j=Next[j];
29         }
30     }
31     return ans;
32 }
33 
34 int main() {
35     for(scanf("%d",&_);_;_--) {
36         scanf("%s",p);
37         scanf("%s",t);
38         printf("%d
",kmp());
39     }
40 }