You are given two lists of closed intervals, firstList and secondList, where firstList[i] = [startᵢ, endᵢ] and secondList[j] = [startⱼ, endⱼ]. Each list of intervals is pairwise disjoint and in sorted order.
Return the intersection of these two interval lists.
A closed interval [a, b] (with a <= b) denotes the set of real numbers x with a <= x <= b.
The intersection of two closed intervals is a set of real numbers that is either empty or represented as a closed interval. For example, the intersection of [1, 3] and [2, 4] is [2, 3].
Example 1:
Input: firstList = [[0,2],[5,10],[13,23],[24,25]], secondList = [[1,5],[8,12],[15,24],[25,26]]
Output: [[1,2],[5,5],[8,10],[15,23],[24,24],[25,25]]
Explanation: The intersections are computed pairwise between overlapping intervals from both lists.
Example 2:
Input: firstList = [[1,3],[5,9]], secondList = []
Output: []
Explanation: One of the lists is empty, so there are no intersections.
Example 3:
Input: firstList = [[1,7]], secondList = [[3,10]]
Output: [[3,7]]
Explanation: The single intervals overlap from 3 to 7.
0 <= firstList.length, secondList.length <= 1000firstList.length + secondList.length >= 10 <= startᵢ < endᵢ <= 10⁹ (except single-point intervals where startᵢ == endᵢ)0 <= startⱼ < endⱼ <= 10⁹ (except single-point intervals where startⱼ == endⱼ)