Merge Overlapping Intervals

Problem

Given an array of intervals where intervals[i] = [start_i, end_i], merge all overlapping intervals, and return an array of the non-overlapping intervals that cover all the intervals in the input.

Examples

merge([[1,3],[2,4],[5,7],[6,8]]);
// returns [[1,4],[5,8]]
// [1,3] and [2,4] are overlapping and are merging into [1,4]
// Same for [5,7] and [6,8], they are merging into [5,8]

merge([[1,8],[6,10]]);
// returns [[1,10]]