Employee Free Time

'''We are given a list schedule of employees, which represents the working time for each employee.

Each employee has a list of non-overlapping Intervals, and these intervals are in sorted order.

Return the list of finite intervals representing common, positive-length free time for all employees, also in sorted order.

(Even though we are representing Intervals in the form [x, y], the objects inside are Intervals, not lists or arrays. 
For example, schedule[0][0].start = 1, schedule[0][0].end = 2, and schedule[0][0][0] is not defined).  
Also, we wouldn't include intervals like [5, 5] in our answer, as they have zero length.'''

"""
# Definition for an Interval.
class Interval(object):
    def __init__(self, start=None, end=None):
        self.start = start
        self.end = end
"""

class Solution(object):
    def employeeFreeTime(self, schedule):
        """
        :type schedule: [[Interval]]
        :rtype: [Interval]
        """
        s = sorted([j for i in schedule for j in i], key=lambda x:x.start)
        
        final = []
        for intl in s:
            if final and intl.start<=final[-1].end:
                final[-1].end = max(final[-1].end, intl.end)
            else:
                final.append(intl)
        
        free = []
        for a in range(1, len(final)):
            free.append(Interval(final[a-1].end, final[a].start))
            
        return(free)