Using `timedelta` can make it easier to work with time.

Example: Calculate how long ago since the last bus departed the station given a bus schedule and a current time

Given a string array schedule that contains all the bus times. Find how long ago the last bus left given a current time.

Input: schedule = ["00:00", "08:30", "12:00", "14:30", "18:45"], time = "14:00"

Output: 120 minutes

Explanation: The last bus left at 12:00pm, which was 2 hours ago

One way to solve this problem is to brute force and use modulo 60 while subtracting time differences. However this would take a lot of time and you can easily introduce bugs. Using timedelta can make it easier to work with time.

Approach

One way to solve this problem is to brute force and use modulo 60 to find remaining minutes while subtracting time differences. However this would take a lot of time and you can easily introduce bugs. Using timedelta can make it easier to work with time.

Here's my approach. First you should convert our schedule from string format to a datetime format importing timedelta from datetime. Timedelta is useful when calculating time. After this step, you would need a condition statement to check if the current time is greater than the schedule bus times. When the condition is broken, you can return the differences between the current time and last bus scheduled time.

>>> from datetime import timedelta
>>> schedule = schedule = ["00:00", "08:30", "12:00", "14:30", "18:45"]
>>> time = "14:00"
>>> s = []
>>> for i in schedule:
...     s.append(i.split(":"))
...     
... 
>>> s
[['00', '00'], ['08', '30'], ['12', '00'], ['14', '30'], ['18', '45']]
>>> tdelta = []
>>> for i in range(len(s)-1):
...     hr, m = s[i]
...     tdelta.append(timedelta(hours=int(hr), minutes=int(m)))
...     
... 
>>> tdelta
[datetime.timedelta(0), datetime.timedelta(seconds=30600), datetime.timedelta(seconds=43200
), datetime.timedelta(seconds=52200)]
>>> hour, minute = time.split(":")
>>> time = timedelta(hours=int(hour), minutes=int(minute))
>>> time
datetime.timedelta(seconds=50400)
>>> prev_bus_diff = [] 
>>> for t in tdelta:
...     if time > t:
...         prev_bus_diff.append(time-t)
...         
...     
... 
>>> ans = min(prev_bus_diff).seconds
>>> ans
7200
>>> int(ans) / 60 # Convert to minutes
120.0