Interval List Intersections

Given two lists of closed intervals, each sorted by start time and pairwise disjoint within a list, return every intersection between the two lists using a two-pointer sweep. A follow-up asks how to handle input lists too large to fit in memory. Interval List Intersections Given two lists of closed intervals, each sorted by start time and pairwise disjoint within a list, return every intersection between the two lists using a two-pointer sweep. A follow-up asks how to handle input lists too large to fit in memory. SWE interval two-pointer array streaming medium Frequency Single report Last asked 2026-01-09 Stage onsite-coding Interval List Intersections You are given two lists of closed intervals, firstList and secondList. Each list is sorted by start time, and the intervals within the same list are pairwise disjoint. Return all intersections between the two lists. An intersection between [a, b] and [c, d] is [max(a, c), min(b, d)] when max(a, c) <= min(b, d). Follow-up note: If the lists are too large to fit in memory, keep the same two-pointer logic but read each list as a stream or chunked iterator, buffering only the current interval from each source. Examples Example 1: Input: firstList = [[0,10],[20,30]], secondList = [[5,8],[15,22]] Output: [[5,8],[20,22]] Example 2: 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]] Constraints 0 <= firstList.length, secondList.length <= 10^5 firstList[i].length == secondList[j].length == 2 0 <= start <= end <= 10^9 firstList and secondList are sorted by start time Intervals inside each list are pairwise disjoint