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Bytedance·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say
May 2026

Summary

Bytedance SWE interview, coding round, one tree DP problem that looks straightforward until you actually try to implement it cleanly under pressure.

Questions Asked (1)

Q1

Given a binary tree where each node holds a non-negative integer value, find the maximum sum you can collect from nodes such that no two chosen nodes are directly connected by a parent-child edge.

Algorithms & Data Structures
Author's notes

I knew this was a tree DP problem pretty quickly but fumbled the state definition at first.

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AI HintsAI Generated

Suggested Approach

Use dynamic programming on the tree, where for each node you compute two values: the maximum sum when the node is included and when it is excluded. Then combine these values bottom-up to get the global maximum.

Pro tip: Clarify that the tree is binary and values are non-negative, which simplifies the DP because excluding a node never forces inclusion of its children. Also, mention that the solution runs in O(n) time and O(h) space for recursion, which is optimal.

1. Define DP states

For each node, define two states: include (max sum if this node is selected) and exclude (max sum if this node is not selected).

2. Establish base cases

For a null node, both include and exclude sums are 0.

3. Recurrence relations

If a node is included, its children must be excluded: include = node.val + left.exclude + right.exclude. If excluded, children can be either included or excluded: exclude = max(left.include, left.exclude) + max(right.include, right.exclude).

4. Post-order traversal

Compute the DP values for each node via a post-order traversal, returning both values from each recursive call.

5. Return final result

At the root, the maximum sum is max(root.include, root.exclude).

Key Points to Mention

  • Dynamic programming on trees (tree DP) with two states per node.
  • Post-order traversal to compute children before parent.
  • Time complexity O(n) and space complexity O(h) for recursion stack.
  • Handling of null nodes as base case.
  • The non-negative values ensure that excluding a node never forces inclusion of children.
  • Comparison with alternative approaches like greedy (which fails) to highlight the need for DP.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.