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Java and recursion

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Join Date: Feb 2006

Posts: 2

Reputation: 3x108th is an unknown quantity at this point

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3x108th

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Newbie Poster

Java and recursion

Feb 11th, 2006

i am working on a program where the user enters a number and the computer will generate N number of characters and print them in all combonations. For example:

enter number: 3

aaa aab aac aba abb abc aca acb acc
baa bab bac bba bbb bbc bca bcb bcc
caa cab cac cba cbb cbc cca ccb ccc

I have made the program build the array and randomize the characters however i dont know how to use recursion to print all the combos. Here is what i have so far:

import cs1.Keyboard;
import java.util.Random;

public class Letter
{

public static void main(String[] args)
{
System.out.println("How many characters do you want");
int number = Keyboard.readInt();

char[] list = new char[number];

Random generator = new Random();

for(int index = 0; index < list.length; index++)
{
int temp = generator.nextInt(26) + 65;
list[index] = (char) temp;
}

//check if all characters are different
for(int index = 0; index < list.length-1; index++)
{
if(list[index] == (list[index+1]))
{
int temp = generator.nextInt(26) + 65;
list[index+1] = (char) temp;
index=0;
}
}
I believe recursion would be the best solution but i dont know how to use it to print the answer. Any help would be great. thanx

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Join Date: Aug 2005

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iamthwee

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Re: Java and recursion

Feb 11th, 2006

This is the basic principle...

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
   char stuff[]="abc";
 
     for(int i=0; i<3; i++)
     {
         for(int j=0; j<3; j++)
         {
             for(int k=0; k<3; k++)
             {
                 print stuff[i];
                 print stuff[j];
                 print stuff[k];
                 print newline
             }
 
         }
     }
   char stuff[]="abc";
     
     for(int i=0; i<3; i++)
     {
         for(int j=0; j<3; j++)
         {
             for(int k=0; k<3; k++)
             {
                 print stuff[i];
                 print stuff[j];
                 print stuff[k];
                 print newline
             }
             
         }
     }

From there you should be able to devise a general model and see where the recursion comes into play.

*Voted best profile in the world*

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Join Date: Feb 2006

Posts: 2

Reputation: 3x108th is an unknown quantity at this point

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3x108th

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Newbie Poster

Re: Java and recursion

Feb 11th, 2006

I understand that. I know thats how it works, but i dont know how to get the for loops to repeat N number of times. The program i am making has to work for any number N.
I'm new at the topic of recursion so im lost in trying to use it. But thanks for the help so for.

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Join Date: Nov 2004

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jwenting

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duckman

Re: Java and recursion

Feb 12th, 2006

so parameterise the whole thing to take a number n instead of using a fixed number of iterations...

As people are clearly allowed to attack me but I'm not allowed to defend myself, I no longer post to this site.

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Join Date: Feb 2006

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masijade

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Nearly a Posting Maven

Re: Java and recursion

Feb 24th, 2006

try the following:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
public void printLoop(int index; char[] list; char[] string) {
  if (index == list.length) {
    System.out.print(new String(string) + " ");
    return;
  }
 
  for (int i = 0; i < list.length; i++) {
    string[index] = list[i];
    printLoop(index + 1, list, string);
  }
}
 
char[] string = new char[list.length];
 
for (int i = 0; i < list.length; i++) {
  string[0] = list[i];
  printLoop(1, list, string);
  System.out.println("");
}
public void printLoop(int index; char[] list; char[] string) {
  if (index == list.length) {
    System.out.print(new String(string) + " ");
    return;
  }

  for (int i = 0; i < list.length; i++) {
    string[index] = list[i];
    printLoop(index + 1, list, string);
  }
}

char[] string = new char[list.length];

for (int i = 0; i < list.length; i++) {
  string[0] = list[i];
  printLoop(1, list, string);
  System.out.println("");
}