How to return a list of values through recursion in java?

Question

Returning a single value through recursion works just fine. But what if I want to return a list of values that recursion goes through each call. Here's my code.

public void inOrder(Node focusNode) {

  /* ArrayList<Integer> tempList = new ArrayList<Integer>(); */

  if ( focusNode != null) {

    inOrder(focusNode.getLeftNode());
    System.out.println(focusNode);
    /*  tempList.add(focusNode.getElement()); */
    inOrder(focusNode.getRightNode());

  }

/*  int[] elems = new int[tempList.toArray().length];
  int i = 0;
  for ( Object o : tempList.toArray()) 
    elems[i++] = Integer.parseInt(o.toString()); */

  //return tempList;
}

printing values while traversing through gives the expected output. But storing those values is not working. It only returns with a single value in a list. Can someone help me with this?

MarsAtomic · Accepted Answer · 2016-07-22 17:07:19Z

1

Why don't you just pass in a reference to an array list along with your starting node? After your inOrder method runs, you'll have an ordered series of values that you can use as you please.

// method signature changed
public void inOrder(Node focusNode, ArrayList vals) {

    /* ArrayList<Integer> tempList = new ArrayList<Integer>(); */

    if ( focusNode != null) {
        // args changed here
        inOrder(focusNode.getLeftNode(), vals);
        // adding node to array list rather than dumping to console
        vals.add(focusNode);
    /*  tempList.add(focusNode.getElement()); */
        inOrder(focusNode.getRightNode());
}

answered Jul 22, 2016 at 17:07

MarsAtomic

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7 Comments

GauravP Over a year ago

Thank you so much ! This is much better way than returning a list. :) One more question, does java also passes variables through reference?

GhostCat Over a year ago

@GauravP Please: if you are able to write such a question here ... then you are also able to put those same strings into a search engine. SO is not "programming school" where teachers explain things to you that are documented a zillion times. This is not meant to be rude; it is just what this site is about ... or not, in this case. In other words: you are expected to do "prior research"; and especially when you are a beginner: please understand that probably any "theoretical" question you can come up with ... was asked here before. And answered. Multiple. Times.

GauravP Over a year ago

@GhostCat I completely get that. Apologies for that. It won't happen again.

MarsAtomic Over a year ago

@GauravP If my answer addressed your question, please click the checkmark on the left side to let future readers know what worked for you. Thanks.

GauravP Over a year ago

@MarsAtomic worked? totally. It saved my 230 lines of code which was completely dependent on this sorted values. Thank You again (Even if stackoverflow suggest me to avoid)!

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