Oulipo（poj3461）（KMP）

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.

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.

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.

#include<stdio.h>
#include<string.h>
#include<algorithm>
using namespace std;
int next[10010],len1,len2;
char a[1000010],s[10010];
void get_next(char *s)
{
	int i=0,j=-1;
	next[0]=-1;
	while(i<len1)
	{
		if(j==-1||s[i]==s[j])
		{
			i++;
			j++;
			next[i]=j;
		}
		else
		    j=next[j];
	}
}
int kmp(char *s,char *a)
{
	get_next(s);
	int i=0,j=0,ans=0;
	while(i<len2)
	{
		if(j==-1||a[i]==s[j])
		{
			i++;
			j++;
		}
		else
		{
			j=next[j];
		}
		if(j==len1)
		{
		    ans++;
		    j=next[j];
		}
	}
	return ans;
}
int main()
{
	int test;
	scanf("%d",&test);
	while(test--)
	{
		scanf("%s%s",s,a);
		len1=strlen(s);
	    len2=strlen(a);
		printf("%d\n",kmp(s,a));
	}
	return 0;
}