From f674f9d7500220571ecf6740e30461af8a7cb351 Mon Sep 17 00:00:00 2001
From: James Mc Dermott <james.mcdermott89@gmail.com>
Date: Sun, 23 Apr 2017 18:44:51 +0100
Subject: [PATCH] Create AVLTree.java

---
 data_structures/AVLTree.java | 212 +++++++++++++++++++++++++++++++++++
 1 file changed, 212 insertions(+)
 create mode 100644 data_structures/AVLTree.java

diff --git a/data_structures/AVLTree.java b/data_structures/AVLTree.java
new file mode 100644
index 000000000..a3bde289f
--- /dev/null
+++ b/data_structures/AVLTree.java
@@ -0,0 +1,212 @@
+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 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();
+    }
+}