poj 3461 Oulipo

【題意】給出子串T,母串s 求子串在母串出現的次數，用KMP算法(hash 以前寫超時)

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<stdio.h>
#include<algorithm>
#include<string.h>
using namespace std;
const int maxn=1e6+10;
int nex[maxn];
char s[maxn],t[maxn];
int n,m;
void getnex(){///nex[]數組獲取 
	int i=1,j=0;
	nex[0]=0;
	while(i<n){
		if(t[i]==t[j])
		nex[i++]=++j;
		else if(!j)
		++i;
		else 
		j=nex[j-1];	
	}
}
int kmp(){//KMP函數 
	int i=0,j=0,ans=0;
	nex[0]=0;
	while(i<n){
		if(s[i]==t[j]){
			++i;
			++j;
		}
		else if(!j)
		++i;
		else
		j=nex[j-1];
		if(j==m){
			ans++;//記錄循環次數 
			j=nex[j-1];//nex[]數組失配總是要返回最近的循環節，若返回j=0會超時 
			
		} 
	}
	return ans;
}
int main(){
	
	int T;
	scanf("%d",&T);
	getchar();
	while(T--){
		scanf("%s%s",&t,&s);
		n=strlen(s);
		m=strlen(t);
		//memset(nex,0,sizeof(nex));
		getnex();
		printf("%d\n",kmp());
	}
}