poj3461Oulipo kmp

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.

求两串中一个串在另一个串中的出现次数

简单kmp系列。直接套模版即可

#include <iostream>
#include <cstring>
#include<cstdio>
using namespace std;
const int N = 1000002;
int nxt[N];
char S[N], T[N];
int slen, tlen;
void getNext()
{
	int j=0,k=-1;nxt[0]=-1;
	while(j<tlen)
	{
		if(k==-1||T[j]==T[k])
			nxt[++j]=++k;
		else
			k=nxt[k];
	}
}
int kmp()
{
	int i=0,j=0,ans=0;
	getNext();
	while(i<slen)
	{
		if(j==-1||S[i]==T[j])
		{
			i++;
			j++;
		}
		else
		{
			j=nxt[j];
		}
		if(j==tlen)
		{
			ans++;
			j=nxt[j];
		}
	}
	return ans;
}
int main()
{

    int n;
    scanf("%d\n",&n);
    while(n--)
	{
	scanf("%s",T);
	scanf("%s",S);
	slen=strlen(S);
	tlen = strlen(T);
	printf("%d\n",kmp());
	}
    return 0;
}