In the Minimum Number of Operations to Convert Time interview question, you are given two strings representing time in "HH:MM" format (24-hour clock). You want to convert the current time to the correct time using the minimum number of operations. An operation consists of adding 1, 5, 15, or 60 minutes to the current time.
Google uses this problem to evaluate basic string parsing and greedy decision-making. It's very similar to the "Change-Making Problem" where you want to provide a specific amount of change using the fewest coins possible. It tests whether you can handle time-to-minute conversion and then apply a standard greedy loop.
This problem utilizes the String, Greedy interview pattern.
diff = correct_minutes - current_minutes.diff to zero by repeatedly subtracting the largest possible increment (60, 15, 5, or 1).Current: "02:30", Correct: "04:35"
A common pitfall is forgetting that the time is in a 24-hour format and not handling the string slicing correctly (e.g., mixing up the hour and minute indices). Another mistake is trying to solve it using BFS or DP, which is unnecessarily complex since the "coin" values (1, 5, 15, 60) are such that the greedy choice is always optimal.
When you encounter a "change-making" style problem, check if the denominations are "canonical." In canonical systems (like most currencies or the 1/5/15/60 time increments), the greedy approach is perfectly optimal and much faster than any other method.