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Bloomberg·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Apr 2026

Summary

Bloomberg coding round, one question, stack-based string decoding. Pretty standard for this kind of interview but the nesting aspect can trip you up if you haven't seen it before.

Questions Asked (1)

Q1

Given an encoded string in the format k[encoded_string] where the substring inside brackets is repeated k times, write a function to decode it. Assume the input is always valid and digits only appear as repeat counts.

Algorithms & Data Structures
Author's notes

The base case is straightforward but I kept second-guessing myself on nested brackets.

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AI HintsAI Generated

Suggested Approach

Use a stack to handle nested encoded strings. Iterate through the input, building the current string and repeat count, and when encountering '[', push the current state onto the stack and reset; when encountering ']', pop and repeat the current string, then append to the previous string.

Pro tip: Clarify edge cases like multi-digit repeat counts and nested brackets, and discuss time/space complexity (O(n) time, O(n) space) to show thoroughness.

1. Understand the problem

Restate the problem and confirm assumptions: input is valid, digits only for repeat counts, and brackets can be nested.

2. Choose data structures

Decide to use a stack to store previous strings and repeat counts for handling nested structures.

3. Iterate and process characters

Loop through each character: if digit, build the repeat count; if letter, append to current string; if '[', push current string and count onto stack and reset; if ']', pop and repeat current string, then append to previous string.

4. Handle multi-digit numbers

Ensure the repeat count is built correctly by accumulating digits (e.g., count = count * 10 + digit).

5. Return the decoded string

After processing all characters, the current string holds the final decoded result.

Key Points to Mention

  • Use of stack for nested structures
  • Handling multi-digit repeat counts
  • Time and space complexity analysis (O(n) time, O(n) space)
  • Edge cases: empty string, no brackets, deeply nested brackets
  • Iterative vs recursive approach trade-offs
  • Potential optimizations like using a string builder to avoid O(n^2) concatenation

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