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.
Example
Input:
[1,2,3,4,5]
1
/ \
2 3
/ \
4 5
Output:
return the root of the binary tree [4,5,2,#,#,3,1]
4
/ \
5 2
/ \
3 1
Clarification:
Confused what[4,5,2,#,#,3,1]
means? Read more below on how binary tree is serialized on OJ.
The serialization of a binary tree follows a level order traversal, where '#' signifies a path terminator where no node exists below.
Here's an example:
1
/ \
2 3
/
4
\
5
The above binary tree is serialized as[1,2,3,#,#,4,#,#,5]
.
Note
题目比较奇怪,本质是把根的左孩子的左孩子置为根的右孩子,根的左孩子的右孩子为根,根左右都变空,对左孩子进行递归
Code
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public TreeNode upsideDownBinaryTree(TreeNode root) {
TreeNode prev = null;
TreeNode curr = root;
TreeNode next = null;
TreeNode temp = null;
while (curr != null) {
next = curr.left;
curr.left = temp;
temp = curr.right; //for next round
curr.right = prev;
prev = curr;
curr = next;
}
return prev;
}
public TreeNode upsideDownBinaryTree2(TreeNode root) {
if (root == null || root.left == null) {
return root;
}
TreeNode newNode = upsideDownBinaryTree(root.left);
root.left.left = root.right;
root.left.right = root;
root.left = root.right = null;
return newNode;
}
}
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