HDU 1686 Oulipo（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.

3
BAPC
BAPC
AZA
AZAZAZA
VERDI
AVERDXIVYERDIAN

1
3
0

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;
#define N 1000005

char a[N],b[N];
int ans,next[N];

void getfail(char *b)
{
	int i,j;
	int len=strlen(b);
	next[0]=-1;
	i=0;j=-1;
	while(i<len)
	{
		if(j==-1||b[i]==b[j])
		{
			i++;
			j++;
			next[i]=j;
		}
		else
			j=next[j];
	}
}

void kmp(char *a,char *b)
{
	int i,j;
	int lena=strlen(a);
	int lenb=strlen(b);
	i=j=0;
	while(i<lena)
	{
		if(j==-1||a[i]==b[j])
		{
			i++;
			j++;
		}
		else
			j=next[j];

		if(j==lenb)
		{
			ans++;
			j=next[j];
		}
	}
}

int main()
{
	int i,j,t;
	scanf("%d",&t);
	while(t--)
	{
		scanf("%s%s",b,a);
		getfail(b);
		ans=0;
		kmp(a,b);
		printf("%d\n",ans);
	}
	return 0;
}