Merge Overlapping Intervals

Given a collection of intervals, merge all overlapping intervals.

1 <= Total number of intervals <= 100000.

First argument is a list of intervals.

Return the sorted list of intervals after merging all the overlapping intervals.

Input 1:

[1,3],[2,6],[8,10],[15,18]

Output 1:

[1,6],[8,10],[15,18]

Explanation 1:

Merge intervals [1,3] and [2,6] -> [1,6].
so, the required answer after merging is [1,6],[8,10],[15,18].
No more overlapping intervals present.