hdu1686之KMP

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

#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<string>
#include<queue>
#include<algorithm>
#include<map>
#include<iomanip>
#define INF 99999999
using namespace std;

const int MAX=1000000+10;
char text[MAX];
char word[10000+10];
int next[10000+10];

void get_next(char *a){//计算next,next会算到next[0...len] 
	int i=0,j=-1,len=strlen(a);
	next[0]=-1;
	while(i<len){
		if(j == -1 || a[i] == a[j]){
			if(a[++i] != a[++j])next[i]=j;
			else next[i]=next[j];//一个优化,表示如果在kmp时a[i]和b[k]不匹配,那么a[i]=a[j],a[j]肯定和b[k]不匹配,所以用next[j]去匹配 
		}else j=next[j];
	}
}

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

int main(){
	int n;
	cin>>n;
	while(n--){
		cin>>word>>text;
		get_next(word);
		cout<<KMP(word,text)<<endl;
	}
	return 0;
}