Merge Intervals

Given an array of intervals 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.

Example 1:

Input:  intervals = [[1,3],[2,6],[8,10],[15,18]]
Output: [[1,6],[8,10],[15,18]]
Explanation: [1,3] and [2,6] overlap → merge to [1,6].

Example 2:

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

Constraints:

• 1 ≤ intervals.length ≤ 10⁴
• intervals[i].length == 2
• 0 ≤ start_i ≤ end_i ≤ 10⁴