Learneroo

Trees and Graphs Comments

Comments

Kendall Ponder
Jul 21, 3:47 PM

If it is best practice to make the node value private why isn't it best practice to make the children nodes private and require methods to access them?
Learneroo
Jul 21, 4:08 PM

It may be "better practice" to do that for the Nodes as well, but its simpler to do these algorithms without creating getters and setters for the Node's children.
Kendall Ponder
Jul 21, 5:30 PM

Thanks!
Salvatore Baglieri
Feb 22, 10:58 AM

I try to use this code https://www.learneroo.com/user_answers/7605767388

but I get back "Main.java:11: error: non-static variable this cannot be referenced from a static context Node node = new Node(ar[i]);"

I am going crazy. Where is the problem?
Learneroo
Feb 22, 11:09 AM

@Salvatore, looking briefly at your code, you should move your Node class out of the Main class (though you'll still have some more work to do).
```
public class Main{
  //all of class Main
}

class Node{
  //all of class Node
}
```
Salvatore Baglieri
Feb 22, 11:17 AM

Ops, thanks! Meanwhile I figured it out by myself.

And I am still fighting to find the solution. Keep (all of) you posted!

mike

static class Node{
Node left;
Node right;
int key;

    Node(int key){
        this.key = key;
    }
}

static void doStuff(int[] ar){
    Node top = ar2SortedTree(ar);

cont...

    printPreOrder(top);
    System.out.println();
}

static void printPreOrder(Node curr){
    if(curr == null) return;

    System.out.print(curr.key + " ");
    printPreOrder(curr.left);
    printPreOrder(curr.right);
}

static void insertKey(Node curr, int key){
    if(key > curr.key){
        if (curr.right != null){
            insertKey(curr.right, key);
        } else {
            curr.right = new Node(key);
        }
    } else if(key < curr.key){
        if (curr.left != null){
            insertKey(curr.left, key);
        } else {
            curr.left = new Node(key);
        }
    }
}

static Node ar2SortedTree(int[] ar){
    if(ar == null || ar.length == 0){
        return null;
    }

    Node top = new Node(ar[0]);

    for(int i = 1; i < ar.length; i++){
        insertKey(top, ar[i]);
    }

    return top;
}

Igor Naverniouk
Sep 17, 3:34 PM

Why is "0 2 3 5 4 1" not a correct answer for input #1?
Learneroo
Sep 17, 3:41 PM

It's a valid BFS, but for this challenge you should visit nodes on one level in the order they were in their line of input.
Igor Naverniouk
Sep 17, 3:49 PM

That's not specified in the problem statement.
Learneroo
Sep 17, 4:04 PM

Thanks. It was mentioned previously, and I updated it so it's mentioned here as well.