Oulipo POJ - 3461（kmp,求重叠匹配个数）

Posted 2022-07-17 dwj-2019

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

 题意：

给出T组数据，每组数据有两个字符串，让我们查找第一个字符串在第二个字符串中出现的次数，可重叠；

思路：kmp；

注意：使用C++中cin、cout作为输入输出语句将导致超时，也是怪坑的

具体代码如下：

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
#define maxx 2000100
char a[maxx],b[10100];
int n,m;
int p[maxx];
void pre()

    int i=0,j=-1;
    p[0]=-1;
    while(i<m)
    
        if(j==-1||b[i]==b[j])
        
            j++,i++;
            p[i]=j;
        
        else
            j=p[j];
    

void kmp()

    int i=0,j=0,ans=0;
    while(i<n)
    
        if(j==-1||a[i]==b[j])
        
            i++,j++;
            if(j==m)
            
                ans++;
                j=p[j];
            
        
        else
            j=p[j];
    
    printf("%d\n",ans);

int main()

    int t;
    scanf("%d",&t);
    while(t--)
    
        scanf("%s%s",b,a);
        n=strlen(a);//
        m=strlen(b);
        pre();
        kmp();
    
    return 0;