My first instinct was brute force all subsets, which is fine given the constraint of at most 16 words, but I wasted time trying to be clever about pruning before I'd even confirmed the basic approach worked.
Start by clarifying the problem and edge cases, then propose a bitmask-based backtracking solution that explores all subsets while pruning invalid concatenations. Discuss time/space complexity and potential optimizations like memoization or DP over masks.
Pro tip: Mention that you can preprocess each string to check for duplicate characters and compute its bitmask, which speeds up the backtracking and shows attention to practical optimization.
Ask questions to confirm constraints: Are all strings lowercase? Can we choose any subset? Is the empty subset allowed? What should be returned if no valid concatenation exists?
For each string, check if it has duplicate characters; if so, discard it. Otherwise, compute a 26-bit mask representing its characters.
Use backtracking to explore subsets, maintaining a combined mask. For each string, if its mask doesn't overlap with the current mask, include it and recurse. Track the maximum length.
Explain that the worst-case time complexity is O(2^n * n) due to exploring all subsets, but pruning reduces practical runtime. Space complexity is O(n) for recursion depth.
Mention memoization (e.g., DP over masks) or sorting strings by length to potentially find a longer concatenation earlier, though the latter doesn't guarantee optimality.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.