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Bytedance·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Jun 2026

Summary

Bytedance SWE interview with an algorithmic problem that starts simple and then asks you to do better. The follow-up is where things get interesting and probably where most people stumble.

Questions Asked (1)

Q1

Given a sorted integer array of length n (n >= 3), find all distinct values that appear strictly more than n/3 times. Return them in increasing order. Then, once you have the linear solution, optimize it to run faster than O(n) using the sorted property.

Algorithms & Data Structures
Author's notes

The base version is fine, just count runs since the array is sorted.

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AI HintsAI Generated

Suggested Approach

First, present the classic Boyer-Moore majority vote algorithm extended to find up to two candidates, then verify their counts in a second pass. For the optimization, leverage the sorted property to binary search for the first and last occurrence of each candidate, or directly check the elements at indices n/3 and 2n/3 to identify potential majority elements.

Pro tip: Emphasize that the sorted array allows you to find candidates by checking the elements at positions floor(n/3) and floor(2n/3), since any element appearing more than n/3 times must cross these boundaries. This insight leads to an O(log n) solution using binary search.

1. Clarify requirements and constraints

Confirm that the array is sorted, n >= 3, and that we need distinct values in increasing order. Discuss edge cases like multiple elements exceeding n/3 (at most two).

2. Present linear solution

Explain the Boyer-Moore majority vote algorithm generalized to two candidates: first pass to find candidates, second pass to verify counts. Mention that it runs in O(n) time and O(1) space.

3. Optimize using sorted property

Describe how to use binary search to find the first and last occurrence of each candidate, or directly check elements at indices n/3 and 2n/3. This reduces time to O(log n) while keeping space O(1).

4. Analyze complexity and trade-offs

Compare the O(n) and O(log n) solutions, noting that the optimized solution relies on the array being sorted and may have higher constant factors but better asymptotic time.

5. Test with examples

Walk through a few examples, such as [1,2,3,3,3] and [1,1,2,2,3,3], to demonstrate correctness and edge cases.

Key Points to Mention

  • Boyer-Moore majority vote algorithm and its extension to two candidates
  • At most two elements can appear more than n/3 times
  • Verification step is necessary because Boyer-Moore only finds candidates
  • Using binary search on sorted array to count occurrences in O(log n)
  • Checking elements at indices n/3 and 2n/3 as potential candidates
  • Time and space complexity trade-offs between O(n) and O(log n) solutions

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