Write a method named mergeIntervals that examines an ordered list of intervals and returns a new list of integers that merges any intervals that overlap.
Your method accepts as its parameter a list of two-element lists of integers, where each sublist represents a [start, end] interval, sorted by starting number.
For example, if the list of existing intervals is [[1, 2], [3, 5], [4, 6], [7, 10], [8, 9], [12, 15]], you should merge the overlapping intervals [3, 5] and [4, 6] into [3, 6] and merge [7, 10] and [8, 9] into [7, 10], to return the list [[1, 6], [7, 10], [12, 15]].
Or if the list of existing intervals is [[1, 3], [2, 3], [4, 8], [5, 6], [7, 10], [10, 14]], you should merge the overlapping intervals to return the list [[1, 3], [4, 14]].
You may assume the input data is valid.
