Invert Binary Tree

L7 Medium Trees

Concept

Tree problems beg for recursion: solve the children first, then combine their answers at the current node.

Given the root of a binary tree, mirror it vertically by swapping the left and right child of every node. Return the root of the inverted tree.

Examples

▸ root = [4, 2, 7, 1, 3, 6, 9]

→ [4, 7, 2, 9, 6, 3, 1]

▸ root = [2, 1, 3]

→ [2, 3, 1]

▸ root = []

→ []

Progressive Hints

Hint 1 · Nudge

Swap at this node, then trust the same recipe on each child.

Hint 2 · Plan

If the root is nil, return nil. Invert both children, then swap the left and right children, and return the root.

Hint 3 · Approach

If root is nil, return nil. Recurse into both children first, then swap them: root.left and root.right trade places. Return root.

Output

// Run your code to see the output here.