Oulipo（KMP）

Oulipo

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 19657		Accepted: 7886

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 textT, 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

    题意：

    给出N，代表有N个输入，每个输入包含两个字符串 w （1 ≤ |W| ≤ 10,000）和 t （ |W| ≤ |T| ≤ 1,000,000），每个输出都输出一个数，代表在 t 中包含有几个 w 子字符串。

 

    思路：

    KMP字符串匹配。注意地方如代码所示。

 

    AC：

#include<stdio.h>
#include<string.h>
char w[10005],t[1000005];
int next[10005],ans,lenw,lent;

void get_next()
{
    int i = 0,j = -1;
    next[0] = -1;
    while(i < lenw)
    {
        if(j == -1 || t[i] == t[j])
        {
            i++;
            j++;
            next[i] = j;
        }
        else j = next[j];
    }
}

void kmp()
{
    int i = 0,j = 0;
    while(i < lent)
    {
        if(j == -1 || t[i] == w[j])
        {
            i++;
            j++;
        }
        else    j = next[j];
        if(j == lenw)
        {
            ans++;
            j = next[j - 1];
            i--；
//注意点，当全部匹配完一个之后，j 序号已经超过模式串长度，所以应该返回前一个的next值，同时 i 也要前移一位与之对应
        }
    }
}

int main()
{
    int n;
    scanf("%d",&n);
    while(n--)
    {
        ans = 0;
        scanf("%s%s",w,t);
        lenw = strlen(w);
        lent = strlen(t);
        get_next();
        kmp();
        printf("%d\n",ans);
    }
    return 0;
}