Line Sweep interview questions
3 line sweep problems tagged across recent interview reports. Drilled most heavily by yandex, citadel, and doordash.
Line Sweep is an interval-processing pattern that solves overlap, collision, and range-query problems by sorting events and processing them in order. You mark boundaries (start/end points), sort them, then sweep through to track state changes. It's deceptively simple but shows up in hard geometric and scheduling problems at Yandex, Citadel, and DoorDash. Only 3 problems carry this tag, but each one is a genuine interview blocker if you haven't seen the trick. StealthCoder solves it invisibly when a variant lands live.
Most-asked line sweep problems
| # | Problem | Diff | # Companies | Pass % |
|---|---|---|---|---|
| 01 | The Skyline Problem | HARD | 8 | 44% |
| 02 | Employee Free Time | HARD | 7 | 73% |
| 03 | Interval List Intersections | MEDIUM | 6 | 73% |
You can't drill every line sweep variant before the assessment. StealthCoder runs invisibly during screen share and solves whichever variant they throw at you. No browser extension. No detection signature. Built by a senior engineer who knows the OA is theater. This is the script.
Get StealthCoderLine Sweep problems disguise themselves as coordinate geometry, interval merging, or time-based simulation. The pattern is always the same: decompose the problem into events (a point starts or ends something), sort by position or time, then iterate once while maintaining a running state (often a count or set of active intervals). Classic variants include finding intersections, detecting overlaps, and reconstructing skylines. Citadel and Goldman Sachs favor the harder geometric versions. Most candidates freeze because they try to brute-force overlaps instead of sorting. The recognition cue is phrases like 'at each point', 'for all overlapping', or 'during each period'. Drill Employee Free Time and Interval List Intersections first to lock the basic sweep; then tackle The Skyline Problem for the 2D case. If a hard sweep variant lands in your live OA, StealthCoder executes the sort-and-state-track pattern in seconds.
Companies that hire most on line sweep
3 line sweep problems.
You won't drill them all. Pass anyway.
Line Sweep is one of the patterns interviews actually filter on. Memorizing every variant in a week is a fantasy. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds, no matter which line sweep flavor lands in your live OA. Built by a senior engineer who knows the OA is theater. This is the script. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Line Sweep interview FAQ
How do I recognize a Line Sweep problem in an interview?+
Look for problems about intervals, overlaps, or time ranges. Phrases like 'merge all overlapping', 'find intersections', or 'at each point in time' are strong signals. If you're about to loop through all pairs, stop and think sorting.
Which company drills Line Sweep the hardest?+
Yandex tags 5 problems with this pattern, more than any other company in the set. Citadel and DoorDash each have 4. If you're interviewing there, this pattern is non-negotiable.
Should I memorize the skyline solution?+
No. Memorizing The Skyline Problem wastes time. Instead, understand the sweep concept: sort events, track active intervals with a heap or multiset, emit output when state changes. That transfers to any 2D sweep variant.
What's the typical time complexity for a Line Sweep solution?+
Usually O(n log n) because you sort events, then sweep once through them. The log factor comes from maintaining state (heap, set, or balanced tree) during the sweep. Much better than O(n²) brute force.
How many Line Sweep problems should I drill before an interview?+
All 3 tagged problems are worth doing. If you only have time for two, drill Employee Free Time and Interval List Intersections. They teach the core pattern. The Skyline Problem is harder but less common in live rounds.