message: Update employee-free-time.py
diff: # Time: O(m * logn), m is the number of schedule, n is the number of employees, m >= n
  # Space: O(n)
  +# 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.
  +#
  +# Example 1:
  +# Input: schedule = [[[1,2],[5,6]],[[1,3]],[[4,10]]]
  +# Output: [[3,4]]
  +# Explanation:
  +# There are a total of three employees, and all common
  +# free time intervals would be [-inf, 1], [3, 4], [10, inf].
  +# We discard any intervals that contain inf as they aren't finite.
  +#
  +# Example 2:
  +# Input: schedule = [[[1,3],[6,7]],[[2,4]],[[2,5],[9,12]]]
  +# Output: [[5,6],[7,9]]
  +# (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.
  +#
  +# Note:
  +# - schedule and schedule[i] are lists with lengths in range [1, 50].
  +# - 0 <= schedule[i].start < schedule[i].end <= 10^8.
  +
  # Definition for an interval.
  # class Interval(object):
  # def __init__(self, s=0, e=0):
  