// Merge Intervals — MEDIUM

// Category: sorting

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.

Hint: Sort by start time, then greedily merge when the current interval overlaps with the previous one.

Example: intervals = [[1,3],[2,6],[8,10],[15,18]]

Output: [[1,6],[8,10],[15,18]]