【LeetCode】156.Binary Tree Upside Down(Medium)(加鎖題)解題報告

【LeetCode】156.Binary Tree Upside Down(Medium)(加鎖題)解題報告

題目地址：https://leetcode.com/problems/binary-tree-upside-down/
題目描述：

  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:

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }

 time : O(n)
 space : O(n)
 */
class Solution {
    public TreeNode upsizeDownBinaryTree(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 = null;
        root.right = null;
        return newRoot;
    }
}

Date：2018年3月17日