Tree Questions at Wix: What to Expect

Tree questions appear in about 12.5% of Wix's technical interview problems (7 out of 56 total). This frequency means you are highly likely to encounter at least one tree-based challenge. Success here demonstrates your grasp of hierarchical data, recursive thinking, and efficient traversal—core skills for front-end developers working with the DOM or back-end engineers handling nested data structures at scale.

What to Expect — Types of Problems

Wix's tree problems typically focus on binary trees, though n-ary trees can appear. Expect questions that test fundamental operations rather than obscure variants. The core categories are:

1. Traversal Problems: You'll be asked to perform in-order, pre-order, post-order, or level-order (BFS) traversals, often to find a node, validate properties, or serialize the structure.
2. Path & Sum Problems: These involve calculating sums along root-to-leaf paths, finding if a path sum matches a target, or identifying common ancestors.
3. Property Validation: Common questions include checking if a tree is a valid Binary Search Tree (BST), determining if it's balanced, or finding its maximum depth/minimum height.
4. Construction & Conversion: You may need to build a tree from given traversal outputs (e.g., from inorder and preorder lists) or convert between tree and other data representations.

The difficulty is usually medium, focusing on clean implementation and optimal time complexity.

How to Prepare — Study Tips with One Code Example

Master the core traversal patterns: Depth-First Search (DFS) using recursion or an explicit stack, and Breadth-First Search (BFS) using a queue. Practice writing these from memory. For recursion, always define your base case first. For problems involving BSTs, leverage the inorder traversal property or use the valid range technique.

A key pattern is the recursive DFS to find maximum depth. This fundamental approach builds intuition for more complex path-based problems.

def maxDepth(root):
    if not root:
        return 0
    left_depth = maxDepth(root.left)
    right_depth = maxDepth(root.right)
    return max(left_depth, right_depth) + 1

Recommended Practice Order

Build competence sequentially. Start with basic traversals (preorder, inorder, postorder, level-order). Next, solve problems about tree properties (max depth, is balanced, is symmetric). Then, tackle path sum and ancestor problems (path sum, lowest common ancestor). Finally, move to construction and conversion problems (build tree from traversals, serialize/deserialize). Within each category, solve easy problems before medium ones.

Practice Tree at Wix