Solved

Randomise An Array of integers

Posted on 2002-03-11
9
214 Views
Last Modified: 2010-03-31
Hi, My problem is that, first of all I have an array that contains integer values. Now, what I want is to shuffle the contents in a random manner.

I tried using the random class and failed by far cause it appears that it allows a certain range that it can select from. I dont need to select any range. I just want to randomise the values that I already have in the array. Hope it is clear and understandable.

Thanx...!!
0
Comment
Question by:q_bic
  • 2
  • 2
  • 2
  • +3
9 Comments
 
LVL 9

Accepted Solution

by:
Venci75 earned 100 total points
ID: 6855726
then - try this:
for (int i = 0; i < arr.length; i++) {
  j = (new java.util.Random()).nextInt(); // random position
  int buff = arr[i];
  arr[i] = arr[j];
  arr[j] = buff;
}
0
 
LVL 27

Expert Comment

by:rrz
ID: 6855744
How about?

import java.io.*;
import java.util.*;
public class Tryrandom
{
public static void main(String args[])
{
 Object numbers[] = {"0","1","2","3","4","5","6","7"};
 ArrayList as = new ArrayList(Arrays.asList(numbers));
 Collections.shuffle(as);
 numbers = as.toArray();
 for (int i=0;i<8;i++)
        System.out.println("result["+i+"]= "+ numbers[i]);
}
}
0
 
LVL 18

Expert Comment

by:bobbit31
ID: 6855745
something like this would work:

          Vector v1 = new Vector();

          for (int i=0;i<100;i++) {
               v1.add(new Integer(i));
          }
         
          Collections.shuffle(v1);
         
          for (int i=0;i<100;i++) {
               out.println(v1.elementAt(i));
          }

0
 
LVL 18

Expert Comment

by:bobbit31
ID: 6855746
damn, too slow ;(
0
How your wiki can always stay up-to-date

Quip doubles as a “living” wiki and a project management tool that evolves with your organization. As you finish projects in Quip, the work remains, easily accessible to all team members, new and old.
- Increase transparency
- Onboard new hires faster
- Access from mobile/offline

 
LVL 7

Expert Comment

by:Igor Bazarny
ID: 6855753
Hi,

> j = (new java.util.Random()).nextInt();
There is no need to create new Random instance each time. And don't let index to go out of range:

Before loop: Random random = new java.util.Random();

Inside loop: j = random.nextInt() % arr.length;

Igor
0
 
LVL 6

Expert Comment

by:gadio
ID: 6855968
Heres an option. This is pseudo code:

java.util.Random r = new java.util.Random();
Object numbers[] = {"0","1","2","3","4","5","6","7"};
for( int cnt = 0; cnt < number.length; cnt++ ) {
   int index = (int)((numbers.length - cnt - 1)* r.nextDouble() + 0.5);
   // do the swap
   int tmp = numbers[cnt];
   numbers[cnt] = numbers[cnt+1+index];
   numbers[cnt+1+index] = tmp;
}

This promis you the following things:
1. Time complexity of o(n).
2. Space complexity of o(n).
3. You will touch each cell of the array at least once.
0
 
LVL 9

Expert Comment

by:Venci75
ID: 6856005
bazarny -> yes - you are right - I forgot this:
j = random.nextInt() % arr.length;
but regarding the new Random() - I used it only for demonstration.

rrz - great suggestion!
0
 

Author Comment

by:q_bic
ID: 6859999
thanx for the great Idea.
0
 
LVL 6

Expert Comment

by:gadio
ID: 6863845
I am sorry to say that after you had accepted the answer, however, the solution by Venci75 is wrong in my opinion.

This:
j = random.nextInt() % arr.length;

is not so good since you may touch any cell, also the ones that you already shuffled. The probability that you will undo shuffles is not zero. This is why in my solution I used:

int index = (int)((numbers.length - cnt - 1)* r.nextDouble() + 0.5);
 
And the range is getting smaller each time - to the ones that were not touched yet.
0

Featured Post

Find Ransomware Secrets With All-Source Analysis

Ransomware has become a major concern for organizations; its prevalence has grown due to past successes achieved by threat actors. While each ransomware variant is different, we’ve seen some common tactics and trends used among the authors of the malware.

Join & Write a Comment

By the end of 1980s, object oriented programming using languages like C++, Simula69 and ObjectPascal gained momentum. It looked like programmers finally found the perfect language. C++ successfully combined the object oriented principles of Simula w…
Introduction This article is the second of three articles that explain why and how the Experts Exchange QA Team does test automation for our web site. This article covers the basic installation and configuration of the test automation tools used by…
Viewers will learn about arithmetic and Boolean expressions in Java and the logical operators used to create Boolean expressions. We will cover the symbols used for arithmetic expressions and define each logical operator and how to use them in Boole…
Viewers will learn about if statements in Java and their use The if statement: The condition required to create an if statement: Variations of if statements: An example using if statements:

758 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

20 Experts available now in Live!

Get 1:1 Help Now