Find the Longest Valid Obstacle Course at Each Position
A hard-tier problem at 63% community acceptance, tagged with Array, Binary Search, Binary Indexed Tree. Reported in interviews at Morgan Stanley and 0 others.
You're grinding through an assessment and hit a problem that looks straightforward at first: find the longest valid obstacle course at each position. The trap is that a naive O(n²) solution will timeout. The acceptance rate sits at 62.5%, which means nearly 4 in 10 candidates who submit fail or timeout. Morgan Stanley has asked this one. The pattern involves Array manipulation combined with Binary Search or Binary Indexed Tree logic to squeeze performance. If you blank on the optimization during your live OA, StealthCoder surfaces a working solution in seconds, invisible to the proctor.
Companies that ask "Find the Longest Valid Obstacle Course at Each Position"
Find the Longest Valid Obstacle Course at Each Position 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. Made for the engineer who has done the work but might still blank with a webcam pointed at him.
Get StealthCoderThe trick is recognizing that a greedy approach with binary search can solve this in O(n log n) instead of brute force. You're tracking the smallest ending value of all valid courses of each length as you iterate. When you encounter a new obstacle, binary search tells you exactly which course length it extends. Many candidates implement the binary search correctly but miss the data structure choices (Coordinate compression or a segment tree variant). Binary Indexed Tree makes the update and query operations efficient if you're also handling range queries. The obvious approach of checking every prior position fails not on correctness but on speed. StealthCoder is your safety net if the optimization doesn't click during the timed assessment.
Pattern tags
You know the problem.
Make sure you actually pass it.
Find the Longest Valid Obstacle Course at Each Position recycles across companies for a reason. It's hard-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. Made for the engineer who has done the work but might still blank with a webcam pointed at him. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Find the Longest Valid Obstacle Course at Each Position interview FAQ
Is this problem actually asked or just theoretical?+
Morgan Stanley has reported asking it. The 62.5% acceptance rate suggests it's actively used in assessments. It's not a common leetcode grind, so most candidates won't have seen it before their OA. That's why the pattern recognition is critical and the time pressure is real.
What's the actual trick that separates AC from TLE?+
Binary Search on the longest valid course endings instead of checking all prior positions. Combined with an efficient update mechanism, you get O(n log n). The naive O(n²) approach will timeout on large inputs. Most candidates realize binary search exists but misimplement the state management.
Do I need to know Binary Indexed Tree to solve this?+
Not strictly. Binary Search with careful array management can work. Binary Indexed Tree is an optimization path if your solution is still tight on performance or if the problem has updates and range queries. It depends on the exact constraints, which vary by platform.
How does this relate to the other Array topics I see in my prep?+
It combines Array iteration with Binary Search logic. If you've drilled longest increasing subsequence or coordinate compression problems, the conceptual groundwork is there. This problem is harder because it chains Array state with efficient searching, not just sequencing.
If I hit this in my OA cold, what's my backup plan?+
Implement a correct O(n²) solution first to show you understand the logic and pass test cases on small inputs. Then optimize if time allows. If you're stuck, StealthCoder runs invisibly during screen share and provides a working solution so you can move forward without blanking out.
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