Bytedance·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

Apr 2026

Summary

Second round for an SRE role at Bytedance that was supposed to cover CS fundamentals but pivoted into a coding problem pretty quickly. Scraped through the visible test cases with some nudging from the interviewer, but probably not a clean pass.

Questions Asked (1)

Given an array of digits representing a number, return the array after adding one to the number.

Algorithms & Data Structures

Author's notes

Did not nail this.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the problem constraints (e.g., no leading zeros except for zero itself, array size limits). Then propose a solution that traverses the array from the end, handling carry propagation, and finally discuss edge cases like all 9s. Optimize for O(n) time and O(1) space if possible.

Pro tip: Mention that you can avoid reversing the array by iterating from the end and using a carry flag, which simplifies the code and reduces overhead. Also, explicitly state that you'll return a new array if the most significant digit overflows (e.g., [9,9,9] -> [1,0,0,0]).

1. Clarify constraints and edge cases

Ask about input size, whether the array can be empty, and if leading zeros are allowed. Confirm that the array represents a non-negative integer.

2. Outline the algorithm

Explain that you'll iterate from the least significant digit (end of array), add 1, and propagate carry. If a digit is less than 9, increment and return; otherwise set to 0 and continue.

3. Handle carry propagation and overflow

If all digits are 9, after the loop, create a new array with length+1, set first element to 1, and rest to 0. Otherwise, return the modified array.

4. Analyze complexity and optimize

State time complexity O(n) and space O(1) for in-place modification (except overflow case). Mention that no extra space is needed for carry.

5. Test with examples

Walk through examples like [1,2,3] -> [1,2,4], [9,9,9] -> [1,0,0,0], and [0] -> [1] to demonstrate correctness.

Key Points to Mention

Carry propagation logic and how to handle it efficiently
Edge cases: all 9s, single digit, empty array (if allowed), and leading zeros
Time and space complexity analysis
In-place modification vs. creating a new array
Avoiding unnecessary array reversal
Potential follow-up: how to handle negative numbers or very large numbers

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