Merge Intervals

Given a collection of intervals, merge all overlapping intervals. Each interval is represented as a pair of integers, where the start and end are both inclusive. Example Input: [[1,3],[2,6],[8,10],[15,18]] Output: [[1,6],[8,10],[15,18]] Input: [[1,4],[4,5]] Output: [[1,5]] Note The input intervals may not be in order. Intervals with the same starting endpoint should be merged if possible. Example Input [[1, 3], [2, 6], [8, 10], [15, 18]]