My first instinct was to mutate the ballots as candidates got eliminated and I wasted a few minutes going down that path before realizing it was a mess.
Clarify the problem and edge cases, then outline a round-based simulation where each round counts first-choice votes among active candidates, checks for a majority, and eliminates the lowest candidate with tie-breaking by lexicographically largest name. Discuss data structures and complexity before coding, and consider optimizations like precomputing ballot rankings or using a priority queue for elimination.
Pro tip: Mention that you can precompute each ballot's ranking as a list of candidate indices and maintain a pointer to the current top active candidate, reducing per-round counting to O(B) and overall complexity to O(B * C) in the worst case.
Ask about input constraints (number of ballots, candidates), tie-breaking rules, and behavior when all candidates tie or when a ballot has no active candidates. Confirm that majority means >50% of active votes.
Simulate rounds: count first-choice votes among active candidates, check for a majority winner, else eliminate the candidate with the fewest votes (tie-break: lexicographically largest name). Repeat until a winner is found.
Use a set for active candidates, a map for vote counts, and precompute ballot rankings to quickly find the top active candidate per ballot. Consider a priority queue for efficient elimination.
Discuss time and space complexity (e.g., O(B * C) time, O(B * C) space). Walk through edge cases: single candidate, all ballots identical, ties, and empty ballots.
Implement the solution cleanly, using helper functions for counting and elimination. Test with provided examples and additional edge cases to ensure correctness.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.