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

分析:

对于树,递归总是是很好的实现方法,所以这题应该

 /**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public TreeNode upsideDownBinaryTree(TreeNode root) {
if (root == null || root.left == null) {
return root;
}
TreeNode newRoot = upsideDownBinaryTree(root.left); root.left.right = root;
root.left.left = root.right; root.left = null;
root.right = null; return newRoot;
}
}
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