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2013
11-12

POJ 3461 Oulipo [解题报告] Java

Oulipo

问题描述 :

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.

输入:

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.

输出:

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.

样例输入:

3
BAPC
BAPC
AZA
AZAZAZA
VERDI
AVERDXIVYERDIAN

样例输出:

1
3
0

解题代码:

//* @author: [email protected]
import java.io.*;
public class Main
{
 static int[] next;
 static String s1,s2;
 static int l1,l2,cnt;
 public static void main(String[] args) throws IOException
 {
  InputStreamReader is=new InputStreamReader(System.in);
  BufferedReader in=new BufferedReader(is);
  int a=Integer.parseInt(in.readLine());
  while((a--)!=0)
  {
	s1=in.readLine();
	s2=in.readLine();
	l1=s1.length();
	l2=s2.length();
	cnt=0;
	next=new int[l1];
	next();
	kmp();
	System.out.println(cnt);
   }
 }

 static void kmp()
 {
  int i=0,j=0;
  while(i< l2&&j< l1)
  {
    if(j==-1||s2.charAt(i)==s1.charAt(j))
    {
	i++;
	j++;
    }
    else j=next[j];
    if(j==l1)
    {
	cnt++;
	i=i-1;
	j=next[j-1];
    }
   }
 }

  static void next() 
  {
   int i = 0;
   next[0] = -1;
   int j = -1;
   while(i < l1 - 1) 
   {
	if(j == -1 || s1.charAt(i) == s1.charAt(j))
	{
		++i;
		++j;
		next[i] = j;
	}
	else
		j = next[j];
    }
  }

}

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