#46 Easy Time O(n) Space O(n) Animated

Invert Binary Tree

Invert a binary tree (mirror it).

LeetCode ↗

Tutor Mode Build the mental model before you memorize the code.

1 Predict
2 Trace
3 Explain
4 Implement

Pattern Tree traversal with recursive contracts

Ask each subtree for exactly the information its parent needs, then combine the two answers.

Approach: DFS (Recursion)

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Core Insight

Ask each subtree for exactly the information its parent needs, then combine the two answers.

Common Pitfall

Define the base case before combining left and right subtree results.

Description

Invert a binary tree (mirror it).

Constraints

Time Complexity: O(n)
Space Complexity: O(n)

Solution — DFS (Recursion)

TimeO(n) SpaceO(n)

Implementation Plan

Translate the invariant into these small, testable moves.

Define what one recursive call returns.
Handle an empty node.
Recurse into children.
Combine the child results at the current node.

def invertTree(root):
    if not root:
        return None
        
    tmp = root.left
    root.left = root.right
    root.right = tmp
    
    invertTree(root.left)
    invertTree(root.right)
    return root

Maximum Depth of Binary Tree

Invert Binary Tree

Steps

Description

Constraints

Tags

Solution — DFS (Recursion)