Intersect Two Sorted Lists of Disjoint Closed Intervals

### Problem Each input list contains sorted, pairwise disjoint closed intervals. Return all nonempty intersections between the two lists, in their natural left-to-right order. Closed endpoints count as included, so an intersection may be a single point `[x,x]` even though each input interval has positive length. ```cpp class Solution { public: vector<vector<int>> intervalIntersection(vector<vector<int>>& firstList, vector<vector<int>>& secondList); }; ``` ### Examples **Example 1:** ```text Input: firstList = [[0,3],[6,9]], secondList = [[3,7]] Output: [[3,3],[6,7]] Explanation: The first contact is the shared endpoint3; the second overlap runs from6 through7. ``` **Example 2:** ```text Input: firstList = [], secondList = [[2,4]] Output: [] Explanation: An empty list contributes no overlap. ``` ### Constraints - `0 <= firstList.length,secondList.length <= 1000`. - Their combined length is at least1. - Every input interval has `0 <= start < end <= 10^9`. - Within each list, every end is strictly less than the next start. ### Contract considerations Within each input list, the end of an interval is strictly less than the next start. ```hint Read the boundary condition After comparing two intervals, the one that ends first cannot help with any future interval in the other list. ``` ### Boundary reminders Within each input list, the end of an interval is strictly less than the next start.