def track_sleep(guard_tracker):
    """Return dictionary that maps guards to the time they are asleep."""
    sleep_tracker = {}
    for key, value in guard_tracker.items():
        guard = key[1]
        if guard not in sleep_tracker:
            sleep_tracker[guard] = []
        for minute, state in enumerate(value):
            if state == '#':
                sleep_tracker[guard].append(minute)

    return sleep_tracker