AVL tree concept added

Trees/AVL.java

@@ -0,0 +1,133 @@
+public class AVL {
+    TreeNode root;
+
+    public class TreeNode { // Copied from leetcode
+        int val;
+        TreeNode left;
+        TreeNode right;
+        TreeNode next;
+
+        TreeNode() {
+
+        }
+
+        TreeNode(int val) {
+            this.val = val;
+        }
+
+        TreeNode(int val, TreeNode left, TreeNode right) {
+            this.val = val;
+            this.left = left;
+            this.right = right;
+        }
+    }
+
+    // Display
+    public void prettyDisplay() {
+        prettyDisplay(root, 0);
+    }
+
+    private void prettyDisplay(TreeNode node, int level) {
+        if (node == null) {
+            return;
+        }
+
+        prettyDisplay(node.right, level + 1);
+        if (level != 0) {
+            // add indentation
+            for (int i = 0; i < level - 1; i++) {
+                System.out.print("|\t\t");
+            }
+            // print the value
+            System.out.println("|------->" + node.val);
+
+        } else {
+            // I'm at root node
+            System.out.println(node.val);
+        }
+        prettyDisplay(node.left, level + 1);
+    }
+
+    // 701. Insert into a Binary Search Tree
+    // TreeNode class doesn't contain height field
+    // Calculate height on the fly instead of storing
+
+    public TreeNode insertIntoBST(TreeNode root, int val) {
+        root = insert(root, val);
+        return root;
+    }
+
+    private TreeNode insert(TreeNode node, int val) {
+
+        if(node == null) {
+            return new TreeNode(val);
+        }
+
+        if(val < node.val) {
+            node.left = insert(node.left, val);
+        } else if (val > node.val) {
+            node.right = insert(node.right, val);
+        } else {
+            return node;
+        }
+
+        return rotate(node);
+    }
+
+    private TreeNode rotate(TreeNode node) {
+
+        int leftHeight = height(node.left);
+        int rightHeight = height(node.right);
+
+        if(leftHeight - rightHeight > 1) {
+
+            if(height(node.left.left) > height(node.left.right)) {
+                return rightRotate(node);
+            }
+
+            node.left = leftRotate(node.left);
+            return rightRotate(node);
+
+        } else if(leftHeight - rightHeight < -1) {
+
+            if(height(node.right.right) > height(node.right.left)) {
+                return leftRotate(node);
+            }
+
+            node.right = rightRotate(node.right);
+            return leftRotate(node);
+        }
+
+        return node;
+    }
+
+    private TreeNode rightRotate(TreeNode p) {
+        TreeNode c = p.left;
+        TreeNode t = c.right;
+
+        c.right = p;
+        p.left = t;
+
+        return c;
+    }
+
+
+    private TreeNode leftRotate(TreeNode c) {
+        TreeNode p = c.right;
+        TreeNode t = p.left;
+
+        p.left = c;
+        c.right = t;
+
+        return p;
+    }
+
+    private int height(TreeNode node) {
+        if(node == null) {
+            return 0;
+        }
+        int leftHeight = height(node.left);
+        int rightHeight = height(node.right);
+        return Math.max(leftHeight, rightHeight) + 1;
+    }
+}