Count Good Triplets in an Array
A hard-tier problem at 66% community acceptance, tagged with Array, Binary Search, Divide and Conquer. Reported in interviews at Walmart Labs and 0 others.
Count Good Triplets hits different when you're staring at an array and three nested loops feel too obvious. Walmart Labs asks this one, and the acceptance rate sits at 66 percent. That's not a giveaway. The trap is brute force: O(n³) will time out on large inputs. You need to recognize when you're counting constrained triplets and pivot to a faster structure. If you blank on the trick during your live OA, StealthCoder runs invisibly and surfaces a working solution in seconds, so you can move on.
Companies that ask "Count Good Triplets in an Array"
Count Good Triplets in an Array 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 core pattern is this: you're counting triplets (i, j, k) where i < j < k and the values satisfy some constraint. Brute force iteration drowns. The real solution uses one of several optimization layers. Binary Search lets you shrink the search space per pair. Merge Sort and Divide and Conquer let you count inversions or constrained elements as you partition. Binary Indexed Tree and Segment Tree are the heavy artillery. They let you query a range in O(log n), turning triplet counting into O(n² log n) or better. Ordered Set is the Pythonic shortcut: maintain sorted structure as you iterate, binary search within it. Most candidates miss the structure entirely and submit brute force first. StealthCoder hedges that moment. The real edge is spotting which optimization fits your constraint shape, then coding it clean.
Pattern tags
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Make sure you actually pass it.
Count Good Triplets in an Array 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. 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.
Count Good Triplets in an Array interview FAQ
Is this actually hard, or does brute force work on smaller test cases?+
Brute force works on small inputs and will pass some test cases, which is the trap. You'll think you're close. Then you hit a large array and time out. That's why it's labeled hard. You must jump to Binary Search, a data structure like Ordered Set, or Merge Sort to pass all cases.
Why does Walmart Labs ask a triplet-counting problem?+
Triplet and n-tuple counting problems test whether you can optimize beyond nested loops. They want to see if you know data structures and divide-and-conquer. It's a proxy for systems thinking and code quality under scale constraints.
What's the fastest real solution?+
Binary Indexed Tree or Segment Tree combined with coordinate compression get you to O(n² log n) or O(n log² n) depending on how tight your constraint is. Merge Sort can also work for certain constraint shapes. The exact optimum depends on your constraint form, which the problem statement defines.
Should I memorize Binary Indexed Tree code for this?+
Not memorize. Understand the pattern: maintain a data structure that answers 'how many elements in range [a, b] have value <= x?' in O(log n). If you get stuck on implementation, StealthCoder will show you a working template. Practice once, then trust the structure.
Is this problem still asked given the 66 percent acceptance rate?+
Yes. High acceptance doesn't mean easy. It means lots of candidates see it in practice, attempt it, and many pass after submitting suboptimal code or getting lucky with test case distribution. Walmart Labs still asks it, so it matters for their pipeline.
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