Merge Intervals

Given a collection of intervals, merge all overlapping intervals. Input: A list of integer intervals. Each interval is a pair of integers [start, end]. Output: Return the list of intervals sorted in ascending order by their start point after merging any overlapping intervals. Example Input: [[1,3],[2,6],[8,10],[15,18]] Example Output: [[1,6],[8,10],[15,18]] Constraints: Number of intervals n satisfies 1 <= n <= 10000, and the start and end of each interval are in the range of 0 to 10000. Example Input [[1,3],[2,6],[8,10],[15,18]]