AVLTree.java

package DataStructures.Trees;

public class AVLTree {

  private Node root;

  private class Node {
    private int key;
    private int balance;
    private int height;
    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;
  }

  private void delete(Node node) {
    if (node.left == null && node.right == null) {
      if (node.parent == null) root = null;
      else {
        Node parent = node.parent;
        if (parent.left == node) {
          parent.left = null;
        } else parent.right = null;
        rebalance(parent);
      }
      return;
    }
    if (node.left != null) {
      Node child = node.left;
      while (child.right != null) child = child.right;
      node.key = child.key;
      delete(child);
    } else {
      Node child = node.right;
      while (child.left != null) child = child.left;
      node.key = child.key;
      delete(child);
    }
  }

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

    while (child != null) {
      node = child;
      child = delKey >= node.key ? node.right : node.left;
      if (delKey == node.key) {
        delete(node);
        return;
      }
    }
  }

  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 n.height;
  }

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

  public void printBalance() {
    printBalance(root);
  }

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

  private void reheight(Node node) {
    if (node != null) {
      node.height = 1 + Math.max(height(node.left), height(node.right));
    }
  }

  public boolean search(int key) {
    Node result = searchHelper(this.root, key);
    if (result != null) return true;

    return false;
  }

  private Node searchHelper(Node root, int key) {
    // root is null or key is present at root
    if (root == null || root.key == key) return root;

    // key is greater than root's key
    if (root.key > key)
      return searchHelper(root.left, key); // call the function on the node's left child

    // key is less than root's key then
    // call the function on the node's right child as it is greater
    return searchHelper(root.right, key);
  }

  public static void main(String[] args) {
    AVLTree tree = new AVLTree();

    System.out.println("Inserting values 1 to 10");
    for (int i = 1; i < 10; i++) tree.insert(i);

    System.out.print("Printing balance: ");
    tree.printBalance();
  }
}