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

Example 1:

    Input: intervals = [[1,3],[2,6],[8,10],[15,18]]
    Output: [[1,6],[8,10],[15,18]]
    Explanation: Since intervals [1,3] and [2,6] overlaps, merge them into [1,6].

Example 2:

    Input: intervals = [[1,4],[4,5]]
    Output: [[1,5]]
    Explanation: Intervals [1,4] and [4,5] are considered overlapping.

Constraints:

- `1 <= intervals.length <= 104`
- `intervals[i].length == 2`
- `0 <= starti <= endi <= 104`