Bytedance·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

May 2026

Summary

Bytedance SWE interview with a sliding window problem that looks straightforward until you actually try to optimize it. One question, but the follow-up pushed for linear time which is where things got interesting.

Questions Asked (1)

Given an array of candy types, find the maximum number of candies you can collect by moving right from any starting position, subject to the constraint that you can only carry at most two distinct types. Follow-up: can you do it in linear time?

Algorithms & Data Structures

Author's notes

Sliding window with two pointers, pretty much textbook.

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AI HintsAI Generated

Suggested Approach

Clarify that this is the 'longest subarray with at most two distinct values' problem, then present a sliding window solution using a hash map to track counts. Explain that the window expands with the right pointer and shrinks from the left when the number of distinct types exceeds two, achieving O(n) time.

Pro tip: Explicitly state the time and space complexity and mention that the algorithm processes each element at most twice, which is optimal for this problem. Also, be prepared to discuss edge cases like empty array or all same type.

1. Clarify the problem

Restate the problem to ensure understanding: find the longest contiguous subarray with at most two distinct integers. Confirm that 'moving right' means contiguous and that we can start at any index.

2. Outline brute force

Briefly mention that a brute force approach would check all subarrays, which is O(n^2) or O(n^3), and is inefficient for large inputs.

3. Introduce sliding window

Explain the sliding window technique: maintain a window [left, right] and a frequency map of elements in the window. Expand right, and while the number of distinct elements > 2, move left and update the map.

4. Detail the algorithm

Walk through the steps: initialize left=0, max_len=0, and an empty map. For each right from 0 to n-1, add arr[right] to map. While map size > 2, decrement count of arr[left], remove if zero, and increment left. Update max_len = max(max_len, right - left + 1).

5. Analyze complexity and edge cases

State that time complexity is O(n) because each element is added and removed at most once, and space is O(1) since the map holds at most 3 distinct elements. Mention edge cases: empty array returns 0, array with <=2 distinct types returns whole length.

Key Points to Mention

Problem is equivalent to 'longest subarray with at most two distinct values'
Sliding window with two pointers (left and right) and a hash map for counts
Condition to shrink: when number of distinct elements exceeds 2
Time complexity O(n) and space O(1) (since map size <= 3)
Each element is processed at most twice (once added, once removed)
Handle edge cases: empty array, array with fewer than 2 distinct types

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