How to Fix Invert Binary Tree Errors

In this tutorial, you'll learn about How to Fix Invert Binary Tree Errors. We cover key concepts, practical examples, and best practices.

Fix invert binary tree errors when swapping order causes null pointer access or partial inversion.

Quick Fix

Wrong

def inv(r):
    if not r: return
    inv(r.left); inv(r.right)
    r.left,r.right=r.right,r.left

Children inverted twice. Results in original tree.

Right

def inv(r):
    if not r: return None
    r.left,r.right=inv(r.right),inv(r.left)
    return r

[4,2,7,1,3,6,9] -> [4,7,2,9,6,3,1]. O(n).

Prevention

Swap before/during recursion. Use iterative BFS for deep trees.

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