Is Invert Binary Tree easy or hard?

Invert Binary Tree is classified as an Easy problem. The logic is straightforward once you understand binary tree traversal, but it effectively tests recursion fundamentals and basic DFS or BFS implementation.

Invert Binary Tree Python/Java solution

Python and Java solutions usually implement a recursive DFS where each call swaps node.left and node.right, then recursively processes both children. The algorithm runs in O(n) time and uses O(h) stack space depending on the tree height.

How to solve Invert Binary Tree in O(n)?

Traverse the tree once and swap the left and right children at every node. This can be done using DFS recursion or BFS with a queue. Since each node is processed a single time, the algorithm runs in O(n) time.

What is the best approach for Invert Binary Tree?

The recursive DFS approach is the most common and concise solution. Swap the left and right children of each node, then recursively process the two subtrees. This visits every node exactly once, giving O(n) time complexity with O(h) recursion stack space where h is the tree height.

Is Invert Binary Tree asked at Google/Amazon/Meta?

Invert Binary Tree is a classic tree traversal problem that has appeared in interviews at companies like Google, Amazon, and Meta. It is commonly used to test understanding of recursion, binary tree structure, and DFS/BFS traversal patterns.

What data structure is used in Invert Binary Tree?

The problem operates on a binary tree data structure. Solutions typically use recursion (DFS with the call stack) or an explicit queue for BFS traversal to visit nodes and swap their children.

What is the time complexity of Invert Binary Tree?

The time complexity is O(n) because each node in the binary tree is visited exactly once and a constant-time swap operation is performed. Space complexity is O(h) for the recursive DFS approach or O(w) for the BFS queue approach, where h is height and w is maximum width.

Description Solution Video 3:55

226. Invert Binary Tree

Easy80.5% acceptance9 companies

Given the root of a binary tree, invert the tree, and return its root.

Example 1:

Input: root = [4,2,7,1,3,6,9]
Output: [4,7,2,9,6,3,1]

Example 2:

Input: root = [2,1,3]
Output: [2,3,1]

Example 3:

Input: root = []
Output: []

Constraints:

The number of nodes in the tree is in the range [0, 100].
-100 <= Node.val <= 100

Asked at 9 companies

Josh Technology Amazon Palo Alto Networks

Google Meta Bloomberg Microsoft Oracle LinkedIn

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3:55

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226. Invert Binary Tree

Asked at 9 companies

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