POJ 3461 Oulipo【kmp】

Oulipo

Time Limit: 1000MS	Memory Limit: 65536K
Total Submissions: 33324	Accepted: 13478

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

思路：

在比對過程中，如果j==lenb，使得j=next【j】即可，因為之前b串和a串過程中有比對完成的部分，一定要省略這些步驟才能保證不會逾時。

ac代碼：

#include<stdio.h>
#include<string.h>
using namespace std;
char b[10002],a[1000002];
int next[1000002];
int lena;
int lenb;
int output;
void set_naxt()//子串的next數組
{
    int i=0,j=-1;
    next[0]=-1;
    while(i<lenb)
    {
        if(j==-1||b[i]==b[j])
        {
            i++; j++;
            next[i]=j;
        }
        else
        j=next[j];
    }
}

int kmp()
{
    int i=0,j=0;
    set_naxt();
    while(i<lena)
    {
        if(j==-1||a[i]==b[j])
        {
            i++;j++;
        }
        else
        j=next[j];
        if(j==lenb)
        {
            output++;
            j=next[j];
            //printf("%d\n",j);
        }
    }
    return -1;
}
int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%s%s",b,a);
        lena=strlen(a);
        lenb=strlen(b);
        output=0;
        kmp();
        printf("%d\n",output);
    }
}