Oulipo （KMP出现次数）

最新推荐文章于 2021-12-04 20:26:59 发布

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最新推荐文章于 2021-12-04 20:26:59 发布

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原文链接：http://www.cnblogs.com/Staceyacm/p/10781820.html

本文深入探讨了KMP算法的原理与实现，通过具体案例展示了如何使用KMP算法高效地在文本中查找特定字符串的出现次数。文章提供了详细的代码示例，并解释了算法的工作流程。

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

KMP板子题

代码：

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

using namespace std;
void kmp_pre(char x[],int m,int next[]) {
	int i,j;
	j=next[0]=-1;
	i=0;
	while(i<m) {
		while(-1!=j && x[i]!=x[j])j=next[j];
		next[++i]=++j;
	}
}
int next[1000010];
int KMP_Count(char x[],int m,char y[],int n) { //x 是模式串，y 是主串
	int i,j;
	int ans=0;
//preKMP(x,m,next);
	kmp_pre(x,m,next);
	i=j=0;
	while(i<n) {
		while(-1!=j && y[i]!=x[j])j=next[j];
		i++;
		j++;
		if(j>=m) {
			ans++;
			j=next[j];
		}
	}
	return ans;
}

char a[10005];
char b[1000005];
int main() {


	int T;
	cin>>T;
	while(T--) {
		scanf("%s",a);
		scanf("%s",b);
		printf("%d\n",KMP_Count(a,strlen(a),b,strlen(b)));
	}


	return 0;
}

转载于:https://www.cnblogs.com/Staceyacm/p/10781820.html