Invert Binary Tree
Detailed guide and Python implementation for the 'Invert Binary Tree' problem.
1. Concept Overview
The 'Invert Binary Tree' problem is a key challenge in the Trees section.
This implementation focuses on medium-level logic in Python.
We prioritize technical accuracy and code readability in our provided solutions.
2. Real-World Applications
3. Visual Intuition
Visualizing the logic flow for Invert Binary Tree.
4. Prerequisites
5. Step-by-Step Thinking
1. Understand the problem
Read the problem statement for Invert Binary Tree carefully.
2. Formulate brute force
Draft a simple iterative solution.
3. Identify inefficiency
Look for redundant calculations.
4. Optimize search path
Use hashing or sorting to speed up the process.
5. Final Implementation
Clean up the code for production standards.
Problem Statement
Given the root of a binary tree, invert the tree, and return its root.
Inverting a binary tree means swapping the left and right children of every node in the tree.
The tree is represented as a level-order list where None represents a missing node. Implement a function invertTree(root: list) -> list that returns the inverted tree in level-order.
- •The number of nodes in the tree is in the range [0, 100]
- •-100 <= Node.val <= 100
Examples
[4,2,7,1,3,6,9]
[4,7,2,9,6,3,1]
The root stays 4. Its children swap: left becomes 7, right becomes 2. Their children also swap recursively.
[2,1,3]
[2,3,1]
The root stays 2. Left child 1 and right child 3 are swapped.
[]
[]
An empty tree inverted is still empty.
Need a Hint?
Edge Cases to Watch
- Empty input structures
- Single element inputs
- Large numerical bounds
Ready to Solve?
Open the problem in PyRun's browser-based Python editor. Your code runs fully offline — no server required.
Interview Insights & Variations
Complexity Analysis Breakdown
Why Time: Directly evaluates all possibilities.
Why Space: Uses standard local memory.
Why Time: Optimized paths reduce total operations.
Why Space: May trade memory for speed.
Optimized Solution Python Code
Optimized Solution Python Code
def invert_tree_opt(root):
if isinstance(root, list):
r = build_tree(root)
res = invert_tree_opt_helper(r)
return tree_to_list(res)
return invert_tree_opt_helper(root)
def invert_tree_opt_helper(root: TreeNode) -> TreeNode:
if not root:
return None
root.left, root.right = invert_tree_opt_helper(root.right), invert_tree_opt_helper(root.left)
return rootBrute Force Code (Spoiler Guarded)
Brute Force Code (Spoiler Guarded)
def invert_tree_brute(root):
if isinstance(root, list):
r = build_tree(root)
res = invert_tree_brute_helper(r)
return tree_to_list(res)
return invert_tree_brute_helper(root)
def invert_tree_brute_helper(root: TreeNode) -> TreeNode:
if not root:
return None
queue = [root]
while queue:
curr = queue.pop(0)
curr.left, curr.right = curr.right, curr.left
if curr.left: queue.append(curr.left)
if curr.right: queue.append(curr.right)
return rootAlgorithm Pattern Checklist
When dealing with Trees data patterns.
Core Prerequisites
Revision Key Notes
Common Mistakes & Pitfalls
Related Questions
Recommended Python Resources
Expand your knowledge with related interactive tutorials, cheat sheets, and code comparisons.
Python Loops
Learn how to use Python loops to iterate over data. Master for loops, while loops, break, continue, and loop best practices with interactive examples.
How to Sort a List in Python
Learn how to sort a list in Python using the sort() method and the sorted() function. Discover custom key sorting and reverse order examples.
Python String Methods
A complete reference guide for Python string manipulation. Master formatting, searching, splitting, replacing, and checking string properties.
Python vs JavaScript: Which Programming Language is Best?
A comprehensive comparison between Python and JavaScript. Explore syntax differences, performance, use cases (backend vs frontend), and coding examples.