Question

I’ve been thinking hard for a long time but couldn’t work this out. Consider the following sequences over time, which records the status of switches:

A = [(10:00, 1), (11:00, 0), (12:00, 1), (12:30, 0),…, (23:00, 1)] # switch A is on at 10:00, off at 11:00 and so on

B = [(10:30, 1), (11:15, 0), (11:30, 1), (12:15, 0),…, (23:30, 0)] # likewise

C = …

(In reality the time is in the format of python’s time.struct_time.)

So basically the structure would be [(time1, status1), (time2, status2)…]. The lists contains data within 24h, and only the switching instances are recorded (so the adjacent “status”es are always opposite to each other). I want to calculate the total amount of time, when all switches A,B,C are on. This seemingly simple question is taking me many days to come up with something useful.

Answer 1

First merge all lists into one list of tuples in the format (time, switch, state). Then sort all the status switches by time, giving a timeline of events.

Then have three variables, a_on, b_on and c_on. Initialize them as the problem specifies (do they start all off or on, etc). Then do something like this:

last_time = 0 # starting time of data, 0 is here as example
total_time = 0 # 0 seconds

for time, switch, state in state_switches:
    if a_on and b_on and c_on:
        total_time += time - last_time

    if switch == "A":
        a_on = state
    if switch == "B":
        b_on = state
    if switch == "C":
        c_on = state

    last_time = time