Poj 3461 Oulipo [KMP]

最新推荐文章于 2020-07-22 02:59:48 发布

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本文介绍了一个基于Oulipo文学概念的文本匹配竞赛，该竞赛要求参赛者编写程序来计算给定单词在一个长文本中出现的次数，涉及字符串处理和KMP算法的应用。

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Oulipo

Poj 3461 Oulipo

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

题意概括：给定两个字符串，输出第一个字符串在第二个字符串中出现的次数。

#include <stdio.h>
#include <string.h>
#define N 1000010
int next[N],f;
 
void get_next(char p[])
{
	int j=0;
	int k=-1;
	next[0]=-1;
	int l=strlen(p);
	while(j<l)
	{
		if(k==-1||p[k]==p[j])
		{
			k++;
			j++;
			next[j]=k;
		}
		else
			k=next[k];
	}
}
void kmp(char s[],char p[])
{
	int j=0;
	int i=0;
	int l1=strlen(s);
	int l2=strlen(p);
	while(i<l1)
	{
		if(s[i]==p[j]||j==-1)
		{
			j++;
			i++;
		}
		else
			j=next[j];//当模式串p读完的时候不会跳出 ，因为while的条件是i<l1,然后读到最后一位的下一位的时候虽然模式串为空了，但是next数组中存的还有一个数就是整个模式串p的最大公共前后缀的大小，所以还会返回继续判断 
		if(j==l2)
			f++;
	}
}
int main()
{
	int t;
	char s[N],p[N];
	scanf("%d",&t);
	getchar();
	while(t--)
	{
		f=0;
		gets(p);
		gets(s);
		get_next(p);
		kmp(s,p);
		printf("%d\n",f);
	}
	return 0;
}