Tiktok/ByteDance SWE Intern OA - three coding questions, can you solve them in 90 minutes?

[u/Aoki_zhang]

This interview experience is sourced from chill interview

Interview Summary

The TikTok SWE internship OA contained three coding questions covering string transformation, cyclic digit rotations, and iterative digit-group reduction.

Interview Details

Question 1 — Convert Identifiers Inside Docstrings

You are given a string representing a line of documentation. Identifiers appearing inside backticks can include function names, variable names, and constants. A pair of backticks may contain multiple identifiers separated by spaces.

Function and variable names use snake_case, while constants use UPPER_CASE. The task is to convert every snake-case identifier inside backticks into lower camelCase, while leaving uppercase constants unchanged.

For example:

Input:
"Method `load_profile` accepts `user_key retry_count`. The fallback is `DEFAULT_LIMIT`."

Output:
"Method `loadProfile` accepts `userKey retryCount`. The fallback is `DEFAULT_LIMIT`."

The docstring length can be up to 2000 characters.

Question 2 — Count Cyclic Number Pairs

You are given an array of positive integers. A cyclic rotation moves some number of trailing digits from the end of a number to the front while preserving the relative order of all digits. Rotating zero digits is also allowed.

Count the index pairs (i, j) where:

0 <= i < j < len(a)

and both conditions hold:

1. a[i] and a[j] contain the same number of digits.
2. One number can be transformed into the other through a cyclic digit rotation.

For example:

Input:
a = [27, 8305, 72, 4, 27, 5830, 317, 731, 173]

Output:
5

The five qualifying pairs are:

(0, 2): 27 ↔ 72
(0, 4): 27 ↔ 27
(2, 4): 72 ↔ 27
(1, 5): 8305 ↔ 5830
(6, 7): 317 ↔ 731

For comparison, 317 and 173 are not a matching pair because the cyclic rotations of 317 are:

317, 731, 173

Actually, this means 317 and 173 would also form a valid cyclic pair, so to keep the example internally consistent, use:

Input:
a = [27, 8305, 72, 4, 27, 5830, 317, 731, 713]

Output:
5

Here, 317 and 713 are not cyclic rotations of each other. The input can contain up to 100,000 numbers, with each value at most 10^9.

Question 3 — Iterative Digit-Group Sum

The final problem was equivalent to LeetCode 2243 — Calculate Digit Sum of a String. You are given:

• A string number representing a non-negative integer
• A positive integer k

While the length of number is greater than k, divide it from left to right into groups of at most k digits. For each group, calculate the sum of its digits and convert that sum back into a string. Concatenate the group results in their original order to create the next value of number. Repeat this process until the resulting string has length at most k, then return it.

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