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Thread: Help generating random permutations from array list

  1. #1
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    Default Help generating random permutations from array list

    There is no output for this code. I don't know why. It seems like it should work. Can someone please let me know what they think i need to change. Here is the problem.

    https://students.ga.desire2learn.com...eeResponse.pdf

     
     
     
    import java.util.Random; //imports the Random java class
    public class PermutationGenerator
     
     
      {
      /*This method iterates the nextPermutation() method 10 times
       *to produce 10 differernt arrays of size 10 with integers
       *1 to 10 inclusive*/
     
      public void PGenerator()
      {
     
      PermutationGenerator a = new PermutationGenerator();
      for (int i=0;i<10;i++) a.nextPermutation();//This loop repeats the nextPermutation method 10 times to produce 10 different arrays
      }
     
      /*This method returns an array of 10 integers from 
       *1 to 10 inclusive in a random order by creating a 
       *new array from permutations of a base array*/
      public int[] nextPermutation()
      {
        Random rand = new Random();//Creates the random generator
        int baseSize = 0;//Initializes the base counter as 0
        int[] base = new int[10];//Initializes the base array
        for (int i = 0; i<10; i++){ //This loop fills up the base array with integers 1 to 10 inclusive
          base[i] = i + 1;
          baseSize++;//Increases the counter for base size
          System.out.println (base);
        }
        int[] mutation = new int[10];//Initializes the mutation array
        for (int i = 0; i<10; i++){
          int a = rand.nextInt(baseSize); //Picks a random index between 0 and the length of the base array
          mutation[i] = base[a]; //Sets the ith index of the result mutation array to the value at a in the base
          for (int j = a; j<baseSize - 1; j++){
            base[j] = base[j + 1];//This loop deletes the value at index a in the base array to prevent it from being chosen again
          System.out.println (base);
          }
          baseSize--;//Decreases the length of the base array
        }
        return mutation;
      }
     
     
     
    public static void main(String[] args)
    {
    }
    }
     
     
    public static void main(String[] args)
    {
    }


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Help generating random permutations from array list

    There is no output for this code
    Add some println statements that print out messages as the code is executed and shows the execution flow and the values of variables as they are changed and used.
    Put the println statements in all the methods so you know what is being executed.
    If you don't understand my answer, don't ignore it, ask a question.

  3. #3
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    Default Re: Help generating random permutations from array list

    i just tried that and not even the first part is being executed.

  4. #4
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    Default Re: Help generating random permutations from array list

    What methods did you see were being executed? What was printed out?
    Did the method that was executed call any other methods?
    Where those other methods executed?
    You'll know when a method is executed when the println statement prints out a message.
    If you don't understand my answer, don't ignore it, ask a question.

  5. #5
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    Default Re: Help generating random permutations from array list

    Nothing is executed. It still doesn't print anything for any step.

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    Default Re: Help generating random permutations from array list

    So take Norm's advice, and locate the first method to be called, and see what it does. Surely at least one method gets called somewhere, sometime, right? Start there.

  7. #7
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    Default Re: Help generating random permutations from array list

    Are there println methods in all the methods? The one in the main() method should print.
    If the main() method doesn't execute, then you must get an error message.
    If you don't understand my answer, don't ignore it, ask a question.

  8. #8
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    Default Re: Help generating random permutations from array list

    I placed a println method at each step and nothing is printed. There is no error message.

  9. #9
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    Default Re: Help generating random permutations from array list

    The one in main() has to print. Can you post the new code that shows where the printlns are located?
    If you don't understand my answer, don't ignore it, ask a question.

  10. #10
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    Default Re: Help generating random permutations from array list

    I edited the original post to reflect changes.

  11. #11
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    Default Re: Help generating random permutations from array list

    Where are the println statements?
    Please post the code with the println statements that you were executing that did not print out anything when it was executed.
    If you don't understand my answer, don't ignore it, ask a question.

  12. #12
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    Default Re: Help generating random permutations from array list

    they are in the code. maybe i did not put them in the right spots? there are two.

  13. #13
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    Default Re: Help generating random permutations from array list

    there are two.
    There should be one in each method at the first thing in the method. You want to see where the code is executing.
    There should be lots of them. 2 is not enough.
    If you don't understand my answer, don't ignore it, ask a question.

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