How hard is LeetCode 1666. Change the Root of a Binary Tree?

LeetCode 1666. Change the Root of a Binary Tree is rated Medium on LeetCode.

What is the time complexity of LeetCode 1666. Change the Root of a Binary Tree?

The Python solution on this page runs in O(V+E).

What is the space complexity of LeetCode 1666. Change the Root of a Binary Tree?

The Python solution on this page uses O(V) auxiliary space.

What topics does LeetCode 1666. Change the Root of a Binary Tree cover?

LeetCode 1666. Change the Root of a Binary Tree is tagged Tree, Depth-First Search and Binary Tree on LeetCode.

Is LeetCode 1666. Change the Root of a Binary Tree a premium problem?

Yes. LeetCode 1666. Change the Root of a Binary Tree is a LeetCode Premium problem, so the full statement and test cases require a paid LeetCode subscription.

Change the Root of a Binary Tree — LeetCode 1666 Python Solution

MediumLeetCode PremiumTreeDepth-First SearchBinary Tree

Problem: #1666
Pattern: Tree Traversal
Reading time: 5 min
Source: leetcode.com

The problem

Given the root of a binary tree and a leaf node, reroot the tree so that the leaf is the new root. You can reroot the tree with the following steps for each node cur on the path starting from the leaf up to the root excluding the root: If cur has a left child, then that child becomes cur's right child.

Example

Input: root = [3,5,1,6,2,0,8,null,null,7,4], leaf = 7
Output: [7,2,null,5,4,3,6,null,null,null,1,null,null,0,8]

Python solution

Python

"""
# Definition for a Node.
class Node:
    def __init__(self, val):
        self.val = val
        self.left = None
        self.right = None
        self.parent = None
"""


class Solution:
    def flipBinaryTree(self, root: "Node", leaf: "Node") -> "Node":
        cur = leaf
        p = cur.parent
        while cur != root:
            gp = p.parent
            if cur.left:
                cur.right = cur.left
            cur.left = p
            p.parent = cur
            if p.left == cur:
                p.left = None
            elif p.right == cur:
                p.right = None
            cur = p
            p = gp
        leaf.parent = None
        return leaf

Complexity

Measure	Complexity
Time	O(V+E)
Space	O(V) auxiliary

Pattern: Tree Traversal

Choose the order — preorder, inorder, postorder, level — and the problem solves itself. LeetCode 1666. Change the Root of a Binary Tree is filed here because LeetCode tags it Tree and Binary Tree, which is the vocabulary this hub collects.

The tree traversal guide has the Python template for the pattern and the 225 LeetCode problems that use it.

Frequently asked questions

How hard is LeetCode 1666. Change the Root of a Binary Tree?: LeetCode 1666. Change the Root of a Binary Tree is rated Medium on LeetCode.
What is the time complexity of LeetCode 1666. Change the Root of a Binary Tree?: The Python solution on this page runs in O(V+E).
What is the space complexity of LeetCode 1666. Change the Root of a Binary Tree?: The Python solution on this page uses O(V) auxiliary space.
What topics does LeetCode 1666. Change the Root of a Binary Tree cover?: LeetCode 1666. Change the Root of a Binary Tree is tagged Tree, Depth-First Search and Binary Tree on LeetCode.
Is LeetCode 1666. Change the Root of a Binary Tree a premium problem?: Yes. LeetCode 1666. Change the Root of a Binary Tree is a LeetCode Premium problem, so the full statement and test cases require a paid LeetCode subscription.