156. Binary Tree Upside Down

Medium (LinkedIn)

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},

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

public class Solution {

public TreeNode upsideDownBinaryTree(TreeNode root) {
    if(root == null || root.left == null && root.right == null) {
        return root;
    }

    TreeNode newRoot = upsideDownBinaryTree(root.left);
    root.left.left = root.right;
    root.left.right = root;
    root.left = root.right = null;
    return newRoot;
}

}