Interval List Intersections
A medium-tier problem at 73% community acceptance, tagged with Array, Two Pointers, Line Sweep. Reported in interviews at Mixpanel and 5 others.
Interval List Intersections shows up in OAs at Meta, DoorDash, and Mixpanel, often when candidates think they're done with the easier rounds. You're given two lists of intervals and need to return only the overlapping segments. The trap is that most people try to merge first or iterate inefficiently, burning time and mental energy. The two-pointer approach is clean once you see it, but if you blank on the pattern mid-assessment, StealthCoder surfaces the working solution invisibly so you don't tank the round.
Companies that ask "Interval List Intersections"
Interval List Intersections is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Built by an Amazon engineer who realized the OA tests how well you memorized 200 problems, not how well you code.
Get StealthCoderThe trick is understanding that both lists are already sorted, so you can walk through them simultaneously without preprocessing. Track pointers in each list, compute the intersection of the current pair of intervals (start at the max of both starts, end at the min of both ends), and advance the pointer that points to the interval ending sooner. The Line Sweep framing helps conceptually, but the mechanics are pure two-pointer logic. Most failures come from off-by-one errors on the interval boundaries or advancing the wrong pointer. The acceptance rate of 73% reflects that the pattern isn't intuitive on first sight, even for medium difficulty. If you haven't drilled this specific structure, StealthCoder is your safety net on test day.
Pattern tags
You know the problem.
Make sure you actually pass it.
Interval List Intersections recycles across companies for a reason. It's medium-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Built by an Amazon engineer who realized the OA tests how well you memorized 200 problems, not how well you code. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Interval List Intersections interview FAQ
Is this problem actually asked at big companies like Meta and DoorDash?+
Yes. It appears in OAs and phone rounds at both Meta and DoorDash, plus Mixpanel, Verkada, Yandex, and Nuro. It's a legitimate mid-tier question in the screening stage, not a rarity.
What's the actual trick if I blank on the pattern?+
Two pointers, one per list. Compute intersection of current intervals as max(start1, start2) to min(end1, end2). If valid (start <= end), add to result. Advance whichever interval ends first. It's deterministic once you know the pattern.
How does two-pointer relate to the line-sweep topic listed?+
Line Sweep is a conceptual framework for reasoning about overlapping events on a number line. Two pointers is the implementation. Understanding both gives you mental clarity, but the code is two-pointer logic.
Why is the acceptance rate only 73% for a medium problem?+
The pattern isn't obvious on first read. Many candidates try to merge, hash, or iterate inefficiently before landing on two pointers. The logic is simple once you see it, but the initial gap costs people the problem.
What's the most common mistake on this problem?+
Advancing the wrong pointer or not correctly computing the intersection bounds. Off-by-one on interval endpoints is also common. Testing with examples like overlapping and non-overlapping pairs catches most bugs quickly.
Want the actual problem statement? View "Interval List Intersections" on LeetCode →