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.
Return the merged intervals **sorted by start value in ascending order**. Intervals that merely touch (one ends exactly where the next begins) are considered overlapping and should be merged.
Example 1
Input:intervals = [[1,3],[2,6],[8,10],[15,18]]
Output:[[1,6],[8,10],[15,18]]
Explanation:[1,3] and [2,6] overlap, so they merge into [1,6].
Example 2
Input:intervals = [[1,4],[4,5]]
Output:[[1,5]]
Explanation:[1,4] and [4,5] touch at 4, which counts as overlapping.