Felt fine parsing the times but I fumbled on the edge case where the current time is exactly on a departure time.
Clarify the problem constraints (e.g., list size, sortedness, time format) and then propose an efficient solution. Convert all times to minutes since midnight, find the maximum departure time that is less than or equal to the current time, and compute the difference. If no such time exists, return -1.
Pro tip: Always discuss edge cases like empty list, multiple buses at the same time, and exact matches. Also, mention that if the list is sorted, binary search can achieve O(log n) time, otherwise O(n) is optimal.
Ask about input size, whether the list is sorted, time format (24-hour, leading zeros), and if multiple buses can have the same departure time. Confirm the definition of 'most recent' (latest departure time that is <= current time).
Convert each HH:MM string to minutes since midnight (e.g., 14:30 -> 870) for easy arithmetic. Also convert the current time similarly.
If the list is unsorted, iterate through all times to find the maximum time <= current time. If sorted, use binary search to find the insertion point and check the previous element.
If a valid departure is found, return current_time - departure_time. If no departure is <= current time, return -1. Consider edge cases like empty list, all buses in the future, and exact match (0 minutes ago).
State time complexity (O(n) for unsorted, O(log n) for sorted) and space complexity (O(1) extra). Walk through a few test cases to verify correctness.
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