How do I convert the data of a Node tree into an ordered ArrayList?

Question

public class Node {
private int data;

public int getData() {
    return data;
}

private Node left;
private Node right;

public Node(int d, Node l, Node r) {
    data = d;
    left = l;
    right = r;
}

// Deep copy constructor
public Node(Node o) {
    if (o == null) return;
    this.data = o.data;
    if (o.left != null) this.left = new Node(o.left);
    if (o.right != null) this.right = new Node(o.right);
}

public List<Integer> toList() {
// Recursive code here that returns an ordered list of the nodes
}

The full class is here: https://pastebin.com/nHwXMVrd

What recursive solution could I use to return an ordered ArrayList of the Integers inside the Node? I've tried a lot of things but I have been having difficulties to find a recursive solution.

Is it a binary search tree ? – Schidu Luca Feb 28 '18 at 09:03 — Schidu Luca, Feb 28 '18 at 09:03
Yes it is a binary search tree – ismael oliva Feb 28 '18 at 09:04 — ismael oliva, Feb 28 '18 at 09:04

Schidu Luca · Answer 1 · 2018-02-28T09:23:44.307

1

Given that you have a bst you can make an inorder traversal on in, this will give you all the elements in increasing order (sorted), an example of how it's done:

 public List<Integer> toList() {
        return createOrderedList(this);
 }

 private List<Integer> createOrderedList(Node root) {
     if(root == null) {
         return new ArrayList<>();
     }

     List<Integer> list = new ArrayList<>();
     list.addAll(createOrderedList(root.left));
     list.add(root.data);
     list.addAll(createOrderedList(root.right));

     return list;
 }

edited Feb 28 '18 at 09:23

answered Feb 28 '18 at 09:16

Schidu Luca

3,897
1
12
27

`return new ArrayList` *or* `Collections.emptyList()`, you should also pin to your answer that this is using recursion, which for a lot of nodes... – Eugene Feb 28 '18 at 10:10
Nice point. About recursion though, I don't think it's a big deal. The maximum number of calls in kept in stack is equal to the height of the tree, which in most cases is somewhat `nlogn`, (unless it's very unbalanced). So you need reaaally big tree to get a `Stackoverflow`, if that was your point. – Schidu Luca Feb 28 '18 at 11:00

score 0 · Accepted Answer · answered Feb 28 '18 at 09:13

0

I am not profficent in Java but this would be the general idea of doing it:

public List<Integer> toList() 
{
   List<Integer> newList = new List<Integer>();
   newList.add(this.data);
   if(left != null)
      newList.addAll(left.toList());
   if(right != null)
      newList.addAll(right.toList());
   return newList;
}

answered Feb 28 '18 at 09:13

Robert

2,407
1
24
35

Brilliant, and I will add Collections.sort(newList); Just to order the list. Looking forward for more efficient solutions! My professor said there is a way to automatically order the list without collections! Thanks. – ismael oliva Feb 28 '18 at 09:18
1

To obtained a ordered list just put this line ```newList.add(this.data);``` after the first ```if```. It will be an inorder traversal :) – Schidu Luca Feb 28 '18 at 12:12

How do I convert the data of a Node tree into an ordered ArrayList?

2 Answers2