Reversing the stack contents

Algorithm:

1. Pop all the elements of stack till it becomes empty.
2. After each recursive call, push the popped element at the bottom of stack.

Time Complexity: O(n^2)
Space Complexity: O(n): For recursion stack.

The Great Tree List Recursion Problem

Reference: http://cslibrary.stanford.edu/109/TreeListRecursion.html

Tree structure allows extensive use of recursion for performing various operations. This property of trees is exploited for converting a given BST into a circular doubly linked list.

Algorithm:

1. Convert left subtree of the tree into a circular doubly linked list.
2. Convert right subtree of the tree into a circular doubly linked list.
3. Append root to the list of left subtree.
4. Append the list of right subtree to the root.