README.md

Problem

Binary Tree Upside Down Given a binary tree where all the right nodes are either leaf nodes with a sibling (a left node that shares the same parent node) or empty, flip it upside down and turn it into a tree where the original right nodes turned into left leaf nodes. Return the new root. For example: Given a binary tree {1,2,3,4,5},

    1
   / \
  2   3
 / \
4   5

return the root of the binary tree [4,5,2,#,#,3,1].

   4
  / \
 5   2
    / \
   3   1  

Solution

Keep a stack of parents, rearrage from bottom to up

Solution 2

a more complicated 'reverse linked list'

1. reverse the root->left links when going down the left subtree

2. rearrange the reversed tree to the desired form