Bloomberg·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

May 2026

Summary

Bloomberg SWE interview with a dynamic programming / backtracking problem that looked cleaner on the surface than it turned out to be. The memoization angle is what separates a working solution from a TLE one.

Questions Asked (1)

Given a string and a dictionary of words, return all possible ways to insert spaces into the string so that every segment is a valid dictionary word. The same dictionary word can be used more than once.

Algorithms & Data Structures

Author's notes

My first instinct was pure backtracking and it worked on small inputs, but I could see where it was going with overlapping subproblems.

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AI HintsAI Generated

Suggested Approach

Use recursion with memoization to explore all possible segmentations, where at each position you try every dictionary word that matches the substring starting there. Cache results for each index to avoid redundant work, and build the output by appending valid segmentations of the remaining suffix.

Pro tip: Clarify whether the output should be a list of strings with spaces or a list of lists of words, and mention that you can optimize by grouping dictionary words by length or using a trie to prune invalid prefixes early.

1. Clarify requirements and edge cases

Confirm the output format (e.g., strings with spaces vs. lists of words), and discuss handling of empty strings, empty dictionary, and words that are not in the dictionary. Also note that words can be reused.

2. Define recursive subproblem

Define a function that returns all valid segmentations of the substring starting at index i. At each step, try every dictionary word that matches the substring from i to i+len(word), and recurse on the remaining suffix.

3. Add memoization

Use a memo table (array or hash map) to store results for each starting index to avoid recomputing the same subproblem. This reduces time complexity from exponential to polynomial in the worst case.

4. Build and return results

Combine the current word with each valid segmentation of the suffix, inserting spaces appropriately. Return the list of all valid segmentations for the starting index.

5. Analyze complexity and optimize

Discuss time and space complexity: O(n * m * L) where n is string length, m is dictionary size, and L is average word length, but memoization can improve it. Mention potential optimizations like using a trie or grouping words by length.

Key Points to Mention

Recursive backtracking with memoization to avoid redundant computations
Time and space complexity analysis, including the impact of memoization
Handling of edge cases such as empty string, empty dictionary, and no valid segmentation
Potential optimizations: trie for prefix matching, grouping words by length, or dynamic programming
Clarifying output format and ensuring the solution meets the interviewer's expectations
Discussing trade-offs between different approaches (e.g., recursion vs. iterative DP)

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