poj 3461 Oulipo

Oulipo

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 26226		Accepted: 10466

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

题目大意：给两个字符串，在目标串里找到模式串的个数。

解题思路：用kmp算法模式匹配，这题特别容易超时，用改进后的next数组。

代码如下:

#include <cstdio>
#include <cstring>
const int maxn=1000010;
int next[10010];
char s[maxn];
char t[10010];
int lent,lens,ans; 
void get_next()
{
    int i=0,j=-1;
    next[0]=-1;
    while(i<lent)
    {
        if(j==-1||t[i]==t[j])
        {
            i++;
            j++;
			if(t[i]!=t[j])
				next[i]=j;
			else
				next[i]=next[j];
        }
        else
            j=next[j];
    }
}
int kmp(int i)
{
	int j=0;
    while(i<lens)
	{
		if(j==-1||t[j]==s[i])
		{
			i++;
			j++;
		}
		else
			j=next[j];
		if(j>=lent)
		{
			ans++;
			j=next[j];
		}
	}
	return ans;
}
int main()
{
    int n;
    scanf("%d",&n);
    while(n--)
    {
		ans=0;
        scanf("%s",t);
		lent=strlen(t);
		scanf("%s",s);
        lens=strlen(s);
		get_next();
		printf("%d\n",kmp(0));
    }
    return 0;
}