0986. Interval List Intersections

https://leetcode.com/problems/interval-list-intersections

Description

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 are 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]]

Example 2:

**Input:** firstList = [[1,3],[5,9]], secondList = []
**Output:** []

Example 3:

**Input:** firstList = [], secondList = [[4,8],[10,12]]
**Output:** []

Example 4:

**Input:** firstList = [[1,7]], secondList = [[3,10]]
**Output:** [[3,7]]

Constraints:

• 0 <= firstList.length, secondList.length <= 1000

• firstList.length + secondList.length >= 1

• 0 <= starti < endi <= 109

• endi < starti+1

• 0 <= startj < endj <= 109

• endj < startj+1

ac