【字符串入门专题1】J

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

3
BAPC
BAPC
AZA
AZAZAZA
VERDI
AVERDXIVYERDIAN

 

Sample Output

1
3
0

题意：用字符串1做模式串，字符串2做匹配串，输出匹配串的总数，允许重叠匹配

思路：kmp模板的套用，我自己思维没转过弯，所以wrong了一次，看了一下别人的题解才知道，允许重叠匹配的话，当匹配到模式串的末尾时，不能直接让j从0重新开始，而是利用next数组，让j回到最大匹配坐标。

#include<cstring>
#include<cstdio>
#define N 1100000
#define M 11000 
char s2[M],s1[N];
int NEXT[M];

void getNext(char s2[],int next[])
{
	int i,j,k;
	k = -1;
	j = 0;
	next[0] = -1;//划重点！！！已经n多次忘记初始化了！！ 
	while(s2[j]!='')
	{
		while(k!=-1&&s2[j]!=s2[k])
			k = next[k];
		k++;
		j++;
		if(s2[k]!=s2[j])
			next[j] = k;
		else
			next[j] = next[k];
	}
	return;
}

void kmp(char s1[],char s2[],int next[])
{
	int i,j,count;
	i = j = count = 0;
	while(s1[i]!='')
	{
		while(j!=-1&&s1[i] != s2[j])
			j = next[j];
		j++;
		i++;
		if(s2[j]=='')
		{
			j = next[j];
			count ++;
		}
	}
	printf("%d
",count);
	return;
}

int main()
{
	int t;
	scanf("%d",&t);
	while(t --)
	{
		scanf("%s",s2);
		scanf("%s",s1);
		getNext(s2,NEXT);
		kmp(s1,s2,NEXT);
	}
	return 0;
}