Tree Questions at Arista Networks: What to Expect

Tree questions appear in roughly 9% of Arista Networks' technical interview problems (4 out of 43 total). While this may seem like a small portion, these problems test fundamental data structure mastery and recursive thinking, which are critical for roles involving network data modeling, configuration tree traversal, or system state management. Success here demonstrates you can handle hierarchical data—a common theme in networking software.

What to Expect — Types of Problems

Arista's tree problems typically focus on practical applications over obscure theory. You can expect:

• Binary Tree Traversal: Implementing iterative and recursive in-order, pre-order, and post-order traversals. Questions may involve validating BST properties or serializing/deserializing tree structures.
• Path and Sum Problems: Finding maximum path sums, checking for paths with a target sum, or summing root-to-leaf numbers. These test your ability to track state during recursion.
• Subtree and Ancestor Analysis: Determining if one tree is a subtree of another, finding the lowest common ancestor (LCA), or calculating node distances. These are highly relevant for network topology and dependency resolution.
• Level-Based (BFS) Operations: Performing zigzag level order traversal, finding the right-side view, or connecting level-order siblings. Breadth-first search is key for exploring network layers.

The problems are often direct implementations of standard algorithms, but interviewers will expect clean, efficient code and clear verbal reasoning.

How to Prepare — Study Tips with One Code Example

Master the core traversal patterns first: recursive DFS, iterative DFS using a stack, and BFS using a queue. Practice drawing small trees (5-7 nodes) to trace your logic before coding. Always discuss time and space complexity.

A key pattern is the recursive DFS helper that returns aggregated information. For example, when checking if a binary tree is balanced (the heights of the two subtrees of any node never differ by more than one), you need to propagate both height and balance status upward.

def isBalanced(root):
    def dfs(node):
        if not node:
            return (True, 0)  # (is_balanced, height)
        left_balanced, left_h = dfs(node.left)
        right_balanced, right_h = dfs(node.right)
        balanced = (left_balanced and right_balanced and
                    abs(left_h - right_h) <= 1)
        return (balanced, 1 + max(left_h, right_h))
    return dfs(root)[0]

Recommended Practice Order

1. Foundations: Master recursive and iterative traversals (pre-order, in-order, post-order, level-order).
2. Property Validation: Practice problems like "Validate Binary Search Tree," "Balanced Binary Tree," and "Symmetric Tree."
3. Path and Sum: Solve "Path Sum," "Maximum Path Sum," and "Sum Root to Leaf Numbers."
4. Ancestor & Subtree: Tackle "Lowest Common Ancestor of a Binary Tree" and "Subtree of Another Tree."
5. Construction & Conversion: Work on "Construct Binary Tree from Preorder and Inorder Traversal" and "Convert Sorted Array to Binary Search Tree."
6. Advanced BFS: Finish with problems like "Binary Tree Zigzag Level Order Traversal" and "Populating Next Right Pointers in Each Node."

Focus on writing bug-free code for these patterns within 20-25 minutes per problem.

Practice Tree at Arista Networks