Added AVL Tree Data Structure and Made appropriate changes in Readme.md

Avl_Tree.py

@@ -0,0 +1,138 @@
+# Python code to insert a node in AVL tree 
+# A Binary Search Tree that gets balanced and achieves O(logn) time in searching for a node
+# Generic tree node class 
+class TreeNode(object): 
+    def __init__(self, val): 
+        self.val = val 
+        self.left = None
+        self.right = None
+        self.height = 1
+
+# AVL tree class which supports the  
+# Insert operation 
+class AVL_Tree(object): 
+
+    # Recursive function to insert key in  
+    # subtree rooted with node and returns 
+    # new root of subtree. 
+    def insert(self, root, key): 
+
+        # Step 1 - Perform normal BST 
+        if not root: 
+            return TreeNode(key) 
+        elif key < root.val: 
+            root.left = self.insert(root.left, key) 
+        else: 
+            root.right = self.insert(root.right, key) 
+
+        # Step 2 - Update the height of the  
+        # ancestor node 
+        root.height = 1 + max(self.getHeight(root.left), 
+                           self.getHeight(root.right)) 
+
+        # Step 3 - Get the balance factor 
+        balance = self.getBalance(root) 
+
+        # Step 4 - If the node is unbalanced,  
+        # then try out the 4 cases 
+        # Case 1 - Left Left 
+        if balance > 1 and key < root.left.val: 
+            return self.rightRotate(root) 
+
+        # Case 2 - Right Right 
+        if balance < -1 and key > root.right.val: 
+            return self.leftRotate(root) 
+
+        # Case 3 - Left Right 
+        if balance > 1 and key > root.left.val: 
+            root.left = self.leftRotate(root.left) 
+            return self.rightRotate(root) 
+
+        # Case 4 - Right Left 
+        if balance < -1 and key < root.right.val: 
+            root.right = self.rightRotate(root.right) 
+            return self.leftRotate(root) 
+
+        return root 
+
+    def leftRotate(self, z): 
+
+        y = z.right 
+        T2 = y.left 
+
+        # Perform rotation 
+        y.left = z 
+        z.right = T2 
+
+        # Update heights 
+        z.height = 1 + max(self.getHeight(z.left), 
+                         self.getHeight(z.right)) 
+        y.height = 1 + max(self.getHeight(y.left), 
+                         self.getHeight(y.right)) 
+
+        # Return the new root 
+        return y 
+
+    def rightRotate(self, z): 
+
+        y = z.left 
+        T3 = y.right 
+
+        # Perform rotation 
+        y.right = z 
+        z.left = T3 
+
+        # Update heights 
+        z.height = 1 + max(self.getHeight(z.left), 
+                        self.getHeight(z.right)) 
+        y.height = 1 + max(self.getHeight(y.left), 
+                        self.getHeight(y.right)) 
+
+        # Return the new root 
+        return y 
+
+    def getHeight(self, root): 
+        if not root: 
+            return 0
+
+        return root.height 
+
+    def getBalance(self, root): 
+        if not root: 
+            return 0
+
+        return self.getHeight(root.left) - self.getHeight(root.right) 
+
+    def preOrder(self, root): 
+
+        if not root: 
+            return
+
+        print("{0} ".format(root.val),end=" ") 
+        self.preOrder(root.left) 
+        self.preOrder(root.right) 
+
+
+# Driver program to test above function 
+myTree = AVL_Tree() 
+root = None
+
+root = myTree.insert(root, 10) 
+root = myTree.insert(root, 20) 
+root = myTree.insert(root, 30) 
+root = myTree.insert(root, 40) 
+root = myTree.insert(root, 50) 
+root = myTree.insert(root, 25) 
+
+"""The constructed AVL Tree would be 
+            30 
+           /  \ 
+         20   40 
+        /  \     \ 
+       10  25    50"""
+
+# Preorder Traversal 
+print("Preorder traversal of the", 
+      "constructed AVL tree is") 
+myTree.preOrder(root) 
+print() 

README.md

@@ -20,6 +20,7 @@ This repository contains Data structures, Algorithms and their common usecases i
 * Segment Tree (For sum) (Java + Python)   [Code](segment_Tree.py)
 * Union Find Data Structures (Disjoint Set Data Structure) [Code](UnionFindDS.py) [Learn](Disjoint_Sets.md)
 * Binary Search Tree [Code](BST.py)
+* AVL Tree [Code](Avl_Tree.py)
 
 ## Learning Python ( the pythonic way)