Employee Free Time

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

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

Return the list of finite intervals representing common, positive-length free time forallemployees, 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 representingIntervalsin the form[x, y], the objects inside areIntervals, not lists or arrays. For example,schedule.start = 1, schedule.end = 2, andscheduleis not defined.)

Also, we wouldn't include intervals like [5, 5] in our answer, as they have zero length.

Note:

1. schedule and schedule[i] are lists with lengths in range [1, 50].
2. 0 <= schedule[i].start < schedule[i].end <= 10^8.

Solution & Analysis

/**
* Definition for an interval.
* public class Interval {
*     int start;
*     int end;
*     Interval() { start = 0; end = 0; }
*     Interval(int s, int e) { start = s; end = e; }
* }
*/
class Solution {
public List<Interval> employeeFreeTime(List<List<Interval>> avails) {
List<Interval> result = new ArrayList<>();
List<Interval> timeLine = new ArrayList<>();
Collections.sort(timeLine, ((a, b) -> a.start - b.start));

Interval temp = timeLine.get(0);
for (Interval each : timeLine) {
if (temp.end < each.start) {