AVL Tree

AVL trees are self-adjusting, height-balanced binary search trees.

An AVL tree is a binary search tree in which every node is height balanced, that is, the difference in the heights of its two subtrees is at most 1.

Balance factor of each node = height of right subtree at that node - height of left subtree at that node
AVL tree is that it is a binary search tree in which each node has a balance factor of -1, 0, or +1 
  
Binary Search Tree can become arbitrary unbalanced tree





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A BST can be called an AVL tree if there is no node that has subtree differing in height with more than one.