poj 3461 KMP模式串匹配

Oulipo
Time Limit: 1000MS   Memory Limit: 65536K
Total Submissions: 33539   Accepted: 13568

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

3
BAPC
BAPC
AZA
AZAZAZA
VERDI
AVERDXIVYERDIAN

Sample Output

1
3
0

题意:第一行输入测试数据的组数,接下来有T组测试数据,每一组先输入模式串,然后输入主串,问模式串在主串中出现的次数。

解题思路:最基础的KMP模式串匹配问题,先求出模式串的 next 数组,然后根据 next 数组遍历主串,避免不必要的匹配

其中next数组的具体 求法 和 含义 

 参考博文:http://blog.csdn.net/liu940204/article/details/51318281

                  http://blog.csdn.net/liu940204/article/details/51333045

具体代码:
#include <stdio.h>
#include <string.h>
char s1[10005];
char s2[1000005];
int next[10005];
void Make_next(int lm)
{
	int i=0,j=-1;
	memset(next,0,sizeof(next));
	next[0]=-1;
	while(i<lm)
	{
		if(j==-1 || s1[i]==s1[j])
		{
			i++; j++;
			next[i]=j;
		}
		else
			j=next[j];
	}
}
int Kmp(int ln,int lm)
{
	Make_next(lm);
	int i=0,j=0;
	int count=0;
	while(i<ln)
	{
		if(j==-1 || s2[i]==s1[j])
		{
			i++; j++;
		}
		else
			j=next[j];
		if(j==lm)
			count++;
	}
	return count;
}
int main()
{
	int T;
	scanf("%d",&T);
	while(T--)
	{
		scanf("\n%s\n%s",s1,s2);
		int ln=strlen(s2);
		int lm=strlen(s1);
		printf("%d\n",Kmp(ln,lm));
	}
	return 0; 
}

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