POJ 3641：Oulipo （KMP

Oulipo Time Limit: 1000MS   Memory Limit: 65536K Total Submissions: 40577   Accepted: 16327 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 Source BAPC 2006 Qualification

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题意：给n组数据，每组数据给出a串和b串，求b串在a串中共出现多少次

题解：KMP模版

贴上代码：

#include<cstdio>
#include<iostream>
#include<cstring>
#include<algorithm>
#define N 100010
using namespace std;

int nextval[N];
int lens,lenp;
char s[N*10],p[N];

void getnext()
{
	int i = 0 , j = -1;
	nextval[0] = -1;
	while(i != lenp)
	{
		if(j == -1 || s[i] == s[j])
			nextval[++i] = ++j;
		else
			j = nextval[j]; 
	}
}

int KMP()
{
	int i = 0 , j = 0 ,count = 0;
	while(i != lens && j != lenp)
	{
		if(s[i] == p[j] || j == -1 )
			++i,++j;
		else
			j = nextval[j];
		if(j == lenp)
		{
			++count;
			j = nextval[j];
		}
	}
	return count;
}

int main()
{
	int ncase,len,ans;
	scanf("%d",&ncase);
	while(ncase--)
	{
		scanf("%s%s",p,s);
		lens = strlen(s);
		lenp = strlen(p);
		getnext();
		ans = KMP();
		printf("%d\n",ans);
	}
}