Merge Intervals

Given a collection of intervals, merge all overlapping intervals. Each interval is represented as a pair of integers [start, end], denoting the interval from start to end. Return a merged list of intervals sorted in ascending order. Assume the given intervals are non-overlapping and sorted by their start time. Test Cases Input: [[1,3],[2,6],[8,10],[15,18]], Output: [[1,6],[8,10],[15,18]] Input: [[1,4],[4,5]], Output: [[1,5]] Input: [], Output: [] Input: [[1,4],[5,6]], Output: [[1,4],[5,6]] Input: [[1,10],[2,3],[4,8]], Output: [[1,10]] Data Constraints Number of intervals: [0, 10000] Each interval [start, end] satisfies 0 ≤ start ≤ end ≤ 10000 Example Input [[1,3],[2,6],[8,10],[15,18]]