‹ DS&A interview · Socratic
DSA · Trees · #89

Invert Binary Tree

Module 44 · difficulty 2/5·⏱ 30:00starts on first keystroke

Given the `root` of a binary tree, invert the tree (swap every node's left and right child, recursively) and return its `root`. Implement the function `invertTree(root)`, where each tree node is `{ val, left, right }` and an empty tree is represented by `null`.

Examples
  • root = [4,2,7,1,3,6,9] → [4,7,2,9,6,3,1] — Every left/right pair is swapped at all levels.
  • root = [2,1,3] → [2,3,1]
  • root = [] → [] — An empty tree inverts to an empty tree.
Constraints
  • · The number of nodes in the tree is in the range [0, 100].
  • · -100 <= Node.val <= 100
  • · The tree may be skewed (effectively a linked list).
Session phases
A · Clarify
B · Approach
C · Complexity
D · Edges
E · Code
F · Tradeoff
G · Score
Phase A — Clarify
Ask questions about input bounds, types, and edge constraints.
Ask the coach clarifying questions about the problem.
When you've covered this phase, advance to the next.