Given the root of a binary tree, flatten the tree into a "linked list":
-The "linked list" should use the same TreeNode class where the right child pointer points to the next node in the list and the left child pointer is always null.
-The "linked list" should be in the same order as a pre-order traversal of the binary tree.
Given the root of a binary tree, flatten the tree into a "linked list":
-The "linked list" should use the same TreeNode class where the right child pointer points to the next node in the list and the left child pointer is always null. -The "linked list" should be in the same order as a pre-order traversal of the binary tree.