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\n",kmp()); 39 } 40 }
原文地址:https://www.cnblogs.com/ACMerszl/p/10263472.html