HDU 1686 Oulipo【KMP】

Problem 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

分析：KMP入门题，求出模式串在给定字符串出现的次数。

code:

#include<stdio.h>
#include<string.h>
char m[10001];
char s[1000001];
int next[10001];
int len1,len2,tot;
void getnext()
{
    int i=0,j=-1;
    next[0]=-1;
    while(i<len2)    //和上一题的不同之处
    {
        if(j==-1||m[i]==m[j])
        {
            i++;j++;
            if(m[i]!=m[j])
                next[i]=j;
            else next[i]=next[j];
        }
        else j=next[j];
    }
}
void kmp()
{
    int i=0,j=0;
    while(i<len1&&j<len2)
    {
        if(s[i]==m[j]||j==-1)
        {
            i++;j++;
        }
        else j=next[j]; 
        if(j>=len2)
        {
            tot++;
            j=next[j];  //关键的地方！！！！
        }
    }
}
int main()
{
    int i,t;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%s%s",m,s);
        len1=strlen(s);
        len2=strlen(m);
        tot=0;
        getnext();
        kmp();
        printf("%d\n",tot);
    }
    return 0;
}