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Bloomberg·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Jun 2026

Summary

Bloomberg SWE coding round, just one algorithm question about the Collatz sequence. Pretty straightforward if you've seen it before, less so if you haven't.

Questions Asked (1)

Q1

Given an integer n, write a function that returns the number of steps needed to reach 1 using these rules: if n is even, divide it by 2; if n is odd, multiply by 3 and add 1.

Algorithms & Data Structures
Author's notes

Classic Collatz conjecture problem.

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AI HintsAI Generated

Suggested Approach

Clarify the problem constraints and edge cases, then implement a straightforward simulation using a loop that applies the Collatz rules until n reaches 1, counting steps. Discuss potential optimizations like memoization for repeated calls and analyze time/space complexity.

Pro tip: Mention that while the Collatz conjecture is unproven, for all practical inputs the sequence terminates; also note that using memoization can drastically improve performance if the function is called multiple times with overlapping sequences.

1. Clarify requirements and edge cases

Ask about input constraints (e.g., n >= 1, integer size) and expected behavior for n=1 (should return 0 steps). Confirm that the function should count steps until reaching 1.

2. Design the algorithm

Use a loop: while n != 1, if n is even, n = n/2; else n = 3*n + 1; increment a step counter. Return the counter.

3. Implement and test

Write clean code with meaningful variable names. Test with small values (e.g., n=1,2,3,6) and verify against known sequences.

4. Analyze complexity and optimizations

Discuss time complexity (proportional to sequence length) and space complexity (O(1) for iterative). Mention memoization to cache results for repeated calls.

5. Consider follow-up questions

Be prepared to discuss the Collatz conjecture, potential integer overflow, and how to handle very large n (e.g., using long or BigInteger).

Key Points to Mention

  • Edge case: n=1 returns 0 steps.
  • Use of iterative loop vs recursion (recursion may cause stack overflow for long sequences).
  • Time complexity is O(k) where k is the number of steps; space complexity O(1).
  • Memoization can optimize multiple calls by caching computed sequences.
  • Potential integer overflow when n is large (3*n+1 may exceed int range).
  • The Collatz conjecture is unproven, but the sequence is believed to always reach 1.

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