from heapq import merge
def getFreeTimes(calender1, dayRange1, calender2, dayRange2, meetingLength):
    # We want to go through the calender values and note whether they are starts or end
    calenders, dayRanges = [calender1, calender2], [dayRange1, dayRange2]
    calTup = []
    for i, cal in enumerate(calenders):
        c = []
        for slot in cal:
            c.append((slot[0],'Start'))
            c.append((slot[1],'End'))
        c.append((dayRanges[i][1], 'Start'))
        calTup.append(c)

    # now we sort all these, since the two list are already sorted we can use
    # heapq.merge which is O(n)
    sortedMarks = list(merge(calTup[0], calTup[1]))

    # Iterate over sorted list, starts add to total and ends minus from total
    # When the total is at 0 both the calanders are free
    total, ans, lastEnd = 0, [], max(dayRange1[0], dayRange2[0])
    for i in range(len(sortedMarks)):
        if sortedMarks[i][1]=='Start':
            if total==0 and (sortedMarks[i][0]-lastEnd)>=meetingLength:
                ans.append([lastEnd, sortedMarks[i][0]])
            total += 1
        else:
            total -= 1
            if total==0:
                lastEnd = sortedMarks[i][0]
    return ans


calender1 = [[9, 10.5],[12, 13],[16, 18]]
dayRange1 = [9, 20]

calender2 = [[10, 11.5],[12.5, 14.5],[14.5,15],[16, 17]]
dayRange2 = [10, 18.5]

meetingLength = .5

expAns = [[11.5, 12], [15, 16], [18, 18.5]]
ans = getFreeTimes(calender1, dayRange1, calender2, dayRange2, meetingLength)

print(ans)
print(ans==expAns)