Problem - Merge Intervals

Given an array of intervals, merge all overlapping intervals and return the non-overlapping result.

Example: $[[1,3], [2,6], [8,10], [15,18]]$ becomes $[[1,6], [8,10], [15,18]]$ because $[1,3]$ and $[2,6]$ overlap. You're solving a foundational interval problem.

While you can solve it with sorting alone, understanding it prepares you for harder interval tree problems. Constraints: up to $10^4$ intervals, values up to $10^4$.