Invert Binary Tree
Recognize the pattern
Brute force idea
The naive version of Invert Binary Tree sounds like this: No simpler alternative — recursion IS the clean approach. That direct path helps you understand the question, but it tends to treat every possibility as brand new instead of learning from earlier steps.
Better approach
The deeper shift in Invert Binary Tree is this: Recursively swap left and right children of every node. Once you hold onto the right piece of information from moment to moment, the problem feels less like trial and error and more like following a shape that was there all along.
Key invariant
At the center of Invert Binary Tree is one steady idea: For each node, swap its children, then recursively invert the subtrees. When you keep that truth intact, each local choice supports the larger solution instead of fighting it.
Watch out for
A common way to get lost in Invert Binary Tree is this: Trying to do it iteratively first — recursion is cleaner and more intuitive here. Most mistakes here are not about syntax; they come from losing track of what your state, pointer, or structure is supposed to mean.