[kuangbin专题] KMP POJ 3461 Oulipo

最新推荐文章于 2020-11-24 12:54:48 发布

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本文介绍了一个字符串匹配问题，挑战者需编写程序，在不使用空格的长文本中寻找特定字符串的出现次数，即使字符串重叠也需计数。文章提供了一个算法示例，包括获取Next数组和KMP算法实现。

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题目链接

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

题目大意：找出主串中有多少子串

注意：每次找到在主串中找到一个子串，就相当于在此位置没有匹配上，因为没有匹配上就会再接着往下匹配

if(j==len2){
     count++;
     j=next[j];
}

AC代码

#include <stdio.h>
#include <string.h>
char a1[1000100],a2[10100];
int next[10100],len1,len2;
void getnext(){
	int j=0,i=-1;
	next[0]=-1;	
	while(j<len2){		
		if(i==-1||a1[j]==a2[i]){
			j++;i++;
			next[j]=i;
		}		
		else i=next[i];
	}
}
int kmp(){
	int count=0;
    int i=0,j=0;
    while(i<len1){
        if(j==-1||a1[i]==a2[j]){
          	i++;
          	j++;
        }
        else j=next[j];
        if(j==len2){
            count++;
            j=next[j];
        }
    }
  return count; 
}
int main(){
	int w;
	scanf("%d",&w);
	getchar();
	while(w--){
		memset(next,0,sizeof(next));
		scanf("%s%s",a2,a1);  //a1主串 
		getchar();
		len1=strlen(a1),len2=strlen(a2);
		getnext();
		printf("%d\n",kmp());
	}
	return 0;
}