hdu 1686---KMP

Posted 2020-09-19 茶飘香~

题目链接

 

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

 

代码如下：

#include <iostream>
#include <algorithm>
#include <cstring>
#include <cstdio>
using namespace std;
int n[10005];
char s[1000005],a[10005];
void kmp(int len)
{
    n[0]=0;
    for(int i=1,k=0;i<len;i++)
    {
        while(k>0&&a[k]!=a[i]) k=n[k-1];
        if(a[k]==a[i]) k++;
        n[i]=k;
    }
}

int main()
{
    ///cout << "Hello world!" << endl;
    int T;
    scanf("%d",&T);
    while(T--)
    {
        scanf("%s%s",a,s);
        int len1=strlen(s);
        int len2=strlen(a);
        kmp(len2);
        int flag=0;
        for(int i=0,j=0;i<len1;i++)
        {
            while(j>0&&a[j]!=s[i]) j=n[j-1];
            if(a[j]==s[i]) j++;
            if(j==len2) flag++;
        }
        printf("%d\n",flag);
    }
    return 0;
}