Find gaps between intervals

You are given a list of integer intervals intervals, where each interval is represented as [start, end] (inclusive), and start <= end.

Two intervals may overlap or touch (e.g., [1,3] and [4,6] touch if you consider integers, because there is no missing integer between 3 and 4). Your task is to find all gaps (missing ranges) between the covered portions of the number line.

More precisely:

1. Consider the union of all intervals.
2. Let minCovered be the smallest integer covered by any interval, and maxCovered be the largest integer covered by any interval.
3. Return a list of all maximal missing integer ranges within [minCovered, maxCovered] that are not covered by the union.

Return the gaps as a list of disjoint intervals [gapStart, gapEnd] (inclusive), sorted by gapStart.

Example

• Input: [[1,3],[7,10],[2,4]]
  • Covered union is [1,4] ∪ [7,10]
  • Gaps within [1,10] are [[5,6]]
• Output: [[5,6]]

Notes / Edge cases

• If the union is already contiguous (no gaps), return [] .
• Overlapping intervals should not create gaps.
• Intervals may be unsorted.

Constraints (reasonable interview assumptions)

• 1 <= len(intervals) <= 2e5
• Interval endpoints fit in 32-bit signed integers.