Bloomberg·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Jun 2026

Summary

Bloomberg SWE interview with a string manipulation problem involving wildcards. Pretty straightforward recursion/backtracking territory but still worth knowing cold.

Questions Asked (1)

Given a string containing '0', '1', and '' characters, replace each '' with either '0' or '1' and return all possible resulting binary strings.

Algorithms & Data Structures

Author's notes

Classic backtracking setup.

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AI HintsAI Generated

Suggested Approach

Use backtracking to explore each character: if it's '0' or '1', keep it and move on; if it's '*', branch into two recursive calls, one replacing it with '0' and the other with '1'. Collect the resulting strings when the end of the string is reached. This naturally generates all possible combinations.

Pro tip: Mention that the number of results is 2^k where k is the number of '*', so the time complexity is O(2^k * n) and space O(2^k * n) for output; this shows you consider efficiency and scalability.

1. Clarify and Define

Confirm the problem: input string with '0', '1', '*'; output all possible binary strings after replacing each '*'. Ask about constraints (e.g., string length, number of '*') to gauge expected complexity.

2. Choose Approach

Decide between backtracking (recursive) or iterative BFS/queue. Backtracking is straightforward and efficient for this problem; explain why it's suitable.

3. Implement Backtracking

Write a recursive function that processes the string index by index. For non-'*', append the character and recurse; for '*', branch into two recursive calls with '0' and '1'. When index reaches end, add the built string to results.

4. Analyze Complexity

State time complexity: O(2^k * n) where k is number of '*' and n is string length, because each combination takes O(n) to build. Space complexity: O(2^k * n) for output plus O(n) recursion stack.

5. Test and Edge Cases

Test with no '*', all '*', empty string, and mixed cases. Ensure no duplicates (none here) and correct order (if required).

Key Points to Mention

Backtracking/recursion as the core technique
Time and space complexity analysis (O(2^k * n))
Handling of non-'*' characters by direct inclusion
Branching logic for '*' (two recursive calls)
Base case: when index reaches end of string
Potential iterative alternative using queue (BFS)

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