#471 · #156 · Binary Tree Upside Down(上下翻转二叉树)

Given the root of a binary tree, turn it upside down: the original leftmost path becomes the new left spine, with each original left child becoming a parent whose right child is the original parent. Return the new root. Constraints: the number of nodes is in [0, 10]; every right node either has a sibling or no children.