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Thread: ArrayList recursion return help

  1. #1
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    Default ArrayList recursion return help

    Hi Forums! Im in need of some help with two problems im trying to attempt.

    So the first problem im doing is the pascal's triangle using arraylist<integer> but when it prints out, it gives me the wrong output.
     
    public ArrayList<Integer> getPascal (ArrayList<Integer> rows)
      {
        if (rows.size() < 0)
          return rows;
     
        ArrayList<Integer> lastRow = new ArrayList<Integer>();
     
        lastRow.add(1);
        System.out.println(lastRow);
     
        for (int i = 1; i <= rows.size(); i++)
        {
          ArrayList<Integer> currentRow = new ArrayList<Integer>();
          currentRow.add(lastRow.get(0));
     
          for (int j = 1; j < i; j++)
          {
            currentRow.add(lastRow.get(j - 1) + lastRow.get(j));
          }
     
          currentRow.add(lastRow.get(i));
          lastRow = currentRow;
          System.out.println(currentRow);
     
        }
        return lastRow;
     
     
      }

    From the error compiler there's something wrong with " if (rows.size() < 0) { return; }. Now i know thats obviously wrong but how could i resolve it into ArrayList<Integer> terms? Ive tried a couple methods but they didnt work as well. For my driver, i just declared a new variable to print the result and it gave me [1] [1] going down a column. If anyone does have time on their hands, how would using one object of arraylist look like?

    Thank you very much!


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    Super Moderator Norm's Avatar
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    Default Re: ArrayList recursion return help

    the error compiler
    Please post the full text of the error message.

    when it prints out, it gives me the wrong output.
    Please post the output and add some comments showing what is wrong with the output
    and show what the output should be.

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    Default Re: ArrayList recursion return help

    For the out put it gave me:

    [1]

    [1]

    Where as the output i want to achieve is

    [1]
    [1] [1]
    [1] [2] [1]

    and so on.

    For the error there is none in this case since i fixed the issue. So what do i need to do in order to achieve that output? Is there a discrepancy in the code?

    Thanks!

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    Default Re: ArrayList recursion return help

    Is there a discrepancy in the code?
    Yes I would say there is if it doesnt' do what you want it to do.

    Try debugging the code by adding printlns to show the values of variables and the execution flow as the program executes. If you know how the program is supposed to execute, the print outs should show you where the problem is.

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