HDU-1686-Oulipo(KMP)

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.

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.

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.

3
BAPC
BAPC
AZA
AZAZAZA
VERDI
AVERDXIVYERDIAN

1
3
0

#include <stdio.h>
#include <string.h>

char s1[10001],s2[1000001];
int next[10001];

int main()
{
    int n,len1,len2,i,j;

    scanf("%d",&n);

    while(n--)
    {
        scanf("%s%s",s1,s2);

        len1=strlen(s1);
        len2=strlen(s2);

        //求next数组
        i=0,j=-1;
        next[0]=-1;
        while(i<len1)
        {
            if(j==-1 || s1[i]==s1[j])
            {
                i++;
                j++;

                if(s1[i]!=s1[j]) next[i]=j;
                else next[i]=next[j];
            }
            else j=next[j];
        }


        int ans=0;
        i=0,j=0;
        while(i<len2 && j<=len1)
        {
            if(j==-1 || s2[i]==s1[j])
            {
                i++;
                j++;
                if(j==len1) ans++;
            }
            else j=next[j];
        }

        printf("%d\n",ans);
    }
}