hdu1686：Oulipo

最新推荐文章于 2023-11-06 10:43:58 发布

张宜强

最新推荐文章于 2023-11-06 10:43:58 发布

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分类专栏： kmp hdu hdu刷题记录

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本文深入解析KMP算法在字符串匹配中的应用，通过实例演示如何快速查找一个字符串在另一个字符串中的出现次数，包括KMP算法的实现原理、代码实现及注意事项。

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http://acm.hdu.edu.cn/showproblem.php?pid=1686

Problem 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

BAPC

AZA

AZAZAZA

VERDI

AVERDXIVYERDIAN

Sample Output

求a字符串在b字符串中出现了几次，kmp算法题，要注意的地方是在匹配完成之后要继续匹配。另一道相似的题https://blog.youkuaiyun.com/qq_41505957/article/details/81713361

#include<stdio.h>
#include<string.h>
#define N 100020
char a[10*N],b[N];
int l1,l2,next[N],ans;
void get_next()
{
	int i,j;
	i=0;
	j=-1;
	next[0]=-1;
	while(i<l2)
	{
		if(j==-1||b[i]==b[j])
		{
			i++;
			j++;
			next[i]=j;
		}
		else
			j=next[j];
	}
}
void kmp()
{
	int i,j;
	i=0;
	j=0;
	get_next();
	while(i<l1)
	{
		if(j==-1||a[i]==b[j])
		{
			i++;
			j++;
		}
		else
			j=next[j];
		if(j>=l2)
        {
            j=next[j];              
            ans++;
        }
	}
}
int main()
{
	int k;
	scanf("%d",&k);
	while(k--)
	{
		ans=0;
		scanf("%s%s",b,a);
		l1=strlen(a);
		l2=strlen(b);
		memset(next,0,sizeof(next));
		kmp();
		printf("%d\n",ans);
	}
	return 0;
}