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Waymo·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say
Jun 2026Remote

Summary

Phone screen for a software engineer role at Waymo. Hadn't touched leetcode in a while and it showed. The interviewer was pretty understanding about it, which honestly made it worse somehow.

Questions Asked (1)

Q1

Given a binary tree and an array, determine whether the array represents a valid root-to-leaf path in the tree.

Algorithms & Data Structures
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AI HintsAI Generated

Suggested Approach

Clarify the problem constraints and edge cases, then propose a recursive DFS solution that traverses the tree while matching the array elements. Discuss time and space complexity, and consider iterative alternatives.

Pro tip: Demonstrate thoroughness by handling edge cases like empty tree, empty array, and arrays longer than the path, and mention that the array must end at a leaf node.

1. Clarify the problem

Ask questions to confirm: Does the array represent the exact sequence from root to leaf? Can the array be empty? What if the tree is empty? Should we consider only root-to-leaf paths, not partial paths?

2. Outline the approach

Propose a recursive DFS that traverses the tree while comparing node values with array elements. At each step, check if the current node matches the array element at the current index.

3. Detail the algorithm

Write a recursive function that takes a node and an index. If the node is null or index is out of bounds, return false. If the node value doesn't match array[index], return false. If it's a leaf and index is the last element, return true. Otherwise, recurse on left and right children with index+1.

4. Analyze complexity

State that time complexity is O(n) in the worst case (visiting each node once) and space complexity is O(h) for recursion stack, where h is tree height.

5. Discuss edge cases and alternatives

Mention handling of empty tree, empty array, array longer than path, and array ending before leaf. Optionally, discuss an iterative BFS/DFS approach using a stack.

Key Points to Mention

  • Recursive DFS with index tracking
  • Base cases: null node, index out of bounds, leaf node with last index
  • Time complexity O(n), space complexity O(h)
  • Edge cases: empty tree, empty array, array length mismatch
  • Iterative alternative using stack
  • Importance of checking leaf condition

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