DEV Community

Cover image for Day 48: AVL Tree
Matt Ryan
Matt Ryan

Posted on

3 3

Day 48: AVL Tree

public class Day48 {

    private Node root;

    private class Node {
        private int key;
        private int balance;
        private Node left, right, parent;

        Node(int k, Node p) {
            key = k;
            parent = p;
        }
    }

    public boolean insert(int key) {
        if (root == null)
            root = new Node(key, null);
        else {
            Node n = root;
            Node parent;
            while (true) {
                if (n.key == key)
                    return false;

                parent = n;

                boolean goLeft = n.key > key;
                n = goLeft ? n.left : n.right;

                if (n == null) {
                    if (goLeft) {
                        parent.left = new Node(key, parent);
                    } else {
                        parent.right = new Node(key, parent);
                    }
                    rebalance(parent);
                    break;
                }
            }
        }
        return true;
    }

    public void delete(int delKey) {
        if (root == null)
            return;
        Node n = root;
        Node parent = root;
        Node delNode = null;
        Node child = root;

        while (child != null) {
            parent = n;
            n = child;
            child = delKey >= n.key ? n.right : n.left;
            if (delKey == n.key)
                delNode = n;
        }

        if (delNode != null) {
            delNode.key = n.key;

            child = n.left != null ? n.left : n.right;

            if (root.key == delKey) {
                root = child;
            } else {
                if (parent.left == n) {
                    parent.left = child;
                } else {
                    parent.right = child;
                }
                rebalance(parent);
            }
        }
    }

    private void rebalance(Node n) {
        setBalance(n);

        if (n.balance == -2) {
            if (height(n.left.left) >= height(n.left.right))
                n = rotateRight(n);
            else
                n = rotateLeftThenRight(n);

        } else if (n.balance == 2) {
            if (height(n.right.right) >= height(n.right.left))
                n = rotateLeft(n);
            else
                n = rotateRightThenLeft(n);
        }

        if (n.parent != null) {
            rebalance(n.parent);
        } else {
            root = n;
        }
    }

    private Node rotateLeft(Node a) {

        Node b = a.right;
        b.parent = a.parent;

        a.right = b.left;

        if (a.right != null)
            a.right.parent = a;

        b.left = a;
        a.parent = b;

        if (b.parent != null) {
            if (b.parent.right == a) {
                b.parent.right = b;
            } else {
                b.parent.left = b;
            }
        }

        setBalance(a, b);

        return b;
    }

    private Node rotateRight(Node a) {

        Node b = a.left;
        b.parent = a.parent;

        a.left = b.right;

        if (a.left != null)
            a.left.parent = a;

        b.right = a;
        a.parent = b;

        if (b.parent != null) {
            if (b.parent.right == a) {
                b.parent.right = b;
            } else {
                b.parent.left = b;
            }
        }

        setBalance(a, b);

        return b;
    }

    private Node rotateLeftThenRight(Node n) {
        n.left = rotateLeft(n.left);
        return rotateRight(n);
    }

    private Node rotateRightThenLeft(Node n) {
        n.right = rotateRight(n.right);
        return rotateLeft(n);
    }

    private int height(Node n) {
        if (n == null)
            return -1;
        return 1 + Math.max(height(n.left), height(n.right));
    }

    private void setBalance(Node... nodes) {
        for (Node n : nodes)
            n.balance = height(n.right) - height(n.left);
    }

    public void printBalance(PrintStream out) {
        printBalance(root, out);
    }

    private void printBalance(Node n, PrintStream out) {
        if (n != null) {
            printBalance(n.left, out);
            out.printf("%s ", n.balance);
            printBalance(n.right, out);
        }
    }


}
Enter fullscreen mode Exit fullscreen mode

Top comments (0)

Great read:

Is it Time to go Back to the Monolith?

History repeats itself. Everything old is new again and I’ve been around long enough to see ideas discarded, rediscovered and return triumphantly to overtake the fad. In recent years SQL has made a tremendous comeback from the dead. We love relational databases all over again. I think the Monolith will have its space odyssey moment again. Microservices and serverless are trends pushed by the cloud vendors, designed to sell us more cloud computing resources.

Microservices make very little sense financially for most use cases. Yes, they can ramp down. But when they scale up, they pay the costs in dividends. The increased observability costs alone line the pockets of the “big cloud” vendors.