How to display flat data structure into hierarchical data structure (Java)?

Question

I have recently faced this question in a practical test for a job .

Suppose you are given a flat data structure like this :

**Category**         **Name**         


        

Answer 1

To be efficient, I'd create something like this:

public class Node
{
  // My name
  public String name;
  // My first child. Null if no children.
  public Node child;
  // The next child after me under the same parent.
  public Node sibling;

  // The top node in the tree.
  public static Node adam;

  // Add first node to tree
  public Node(String name)
  {
    this.name=name;
    this.child=null;
    this.sibling=null;
    adam=this;
  }

  // Add a non-Adam node to the tree.
  public Node(String name, Node parent)
  {
    // Copy my name. Easy part.
    this.name=name;
    // Make me the first child of my parent. The previous first child becomes
    // my sibling. If the previous first child was null, fine, now my sibling is null.
    // Note this means that children always add to the front. If this is undesirable,
    // we could make this section a little more complicated to impose the desired
    // order.
    this.sibling=parent.child;
    parent.child=this;
    // As a new node, I have no children.
    this.child=null;
  }
  // Print the current node and all nodes below it.
  void printFamily(int level)
  {
    // You might want a fancier print function than this, like indenting or
    // whatever, but I'm just trying to illustrate the principle.
    System.out.println(level+" "+name);
    // First process children, then process siblings.
    if (child!=null)
      child.printFamiliy(level+1);
    if (sibling!=null)
      sibling.printFamily(level);
  }
  // Print all nodes starting with adam
  static void printFamily()
  {
    adam.printFamily(1);
  }
  // Find a node with a given name. Must traverse the tree.
  public static Node findByName(String name)
  {
    return adam.findByName(name);
  }
  private Node findByNameFromHere(String name)
  {
    if (this.name.equals(name))
      return this;
    if (child!=null)
    {
      Node found=child.findByNameFromHere(name);
      if (found!=null)
        return found;
    }
    if (sibling!=null)
    {
      Node found=sibling.findByNameFromHere(name);
      if (found!=null)
        return found;
    }
    return null;
  }
  // Now we can add by name
  public Node(String name, String parentName)
  {
    super(name, findByName(parentName));
  }
}

Usual disclaimer: This code is off the top of my head, completely untested.

If I was doing this for a real application, I would include error checking and no doubt all sorts of peripheral stuff.