Maximum Number of Pairs in Array
A easy-tier problem at 76% community acceptance, tagged with Array, Hash Table, Counting. Reported in interviews at Altimetrik and 0 others.
Maximum Number of Pairs in Array is an easy problem that tests whether you can count efficiently and extract value from a hash structure. You get an array, you need to find how many pairs you can form from matching elements, then return the pair count plus any leftover singleton. Altimetrik has asked it. The acceptance rate is solid at 75%, which means most people who sit down and code it get it right. That's either because the pattern is obvious once you see it, or because candidates are walking in prepared. Either way, if this hits your live assessment and you blank on the implementation, StealthCoder surfaces a working solution in seconds, invisible to the proctor.
Companies that ask "Maximum Number of Pairs in Array"
Maximum Number of Pairs in 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 engineer who got tired of watching his cohort grind for six months and still get filtered at the OA stage.
Get StealthCoderThe trick is simple: count the frequency of each element, then divide each frequency by 2 to get pairs. Sum all the pair counts. If you have leftover singleton elements (any element with odd frequency), you can form one more pair from them only if you have at least two singletons total. The naive approach is to sort and iterate, but that's slower. Hash Table counting is the pattern here. Count frequencies, iterate through the map, accumulate pairs from each frequency, then handle the leftover logic. Common pitfall: forgetting that leftover singletons only form a pair if there are at least two of them. The problem seems trivial once you see the counting-based approach, which is why acceptance is high. If you freeze on the exact leftover logic during your OA, StealthCoder handles it.
Pattern tags
You know the problem.
Make sure you actually pass it.
Maximum Number of Pairs in Array recycles across companies for a reason. It's easy-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 engineer who got tired of watching his cohort grind for six months and still get filtered at the OA stage. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Maximum Number of Pairs in Array interview FAQ
How hard is this problem really?+
It's genuinely easy. 75% acceptance backs that up. You count frequencies with a hash table, divide by 2, sum the pairs, then add 1 if you have at least 2 singleton leftovers. No recursion, no graph search, no dynamic programming. If you can code a hash-based frequency counter, you can solve this.
What topics should I review before attempting it?+
Array iteration and Hash Table counting are the core. You don't need Counting as a discrete skill separate from hash-map operations. If you're comfortable iterating an array and using a map to track frequency, you have everything. Spend time on the leftover-singleton logic to avoid off-by-one errors.
Is Altimetrik still asking this in their assessments?+
It's reported from Altimetrik. We can't guarantee recency or frequency, but single-company problems tend to stay in rotation if they passed the bar. The low report volume suggests it's not a top-tier favorite, but it could appear in their screening round without warning.
What's the most common mistake candidates make?+
Mishandling the leftover singleton rule. Candidates count pairs correctly but then add leftover singletons incorrectly. You only form one additional pair from singletons if you have 2 or more total singletons. If you have 3 leftovers, you get 1 pair plus 1 unpaired element. Lock that rule in before your OA.
Should I worry about hash collisions or performance?+
No. The problem is straightforward enough that standard hash-table performance is fine. You iterate the array once to count, then iterate the hash table once to sum pairs. O(n) time, O(n) space. No corner cases around collision handling or bucket sizing matter here.
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