https://leetcode.com/problems/is-subsequence/description/

Given two sorted, non-overlapping list of intervals, merge them to produce a single list of sorted, non-overlapping intervals. Example:

Input:

list1 = {[1,2], [3,9]}

list2 = {[4,6], [8,10], [11,12]}

Output should be:

mergedList = {[1,2], [3,10], [11,12]}