Triplets With Unique Chars
Reported by candidates from ZipRecruiter's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
ZipRecruiter's March 2025 OA included a string problem called Triplets With Unique Chars. You're looking at a constraint-based filtering task: given some collection of triplets or strings, find or count those where all three characters are distinct. It's not a trick problem, but the implementation matters. Most candidates over-complicate the uniqueness check or misread what "triplet" means in context. If you blank on the exact logic during the live OA, StealthCoder reads the problem and delivers the pattern in seconds.
Pattern and pitfall
The core pattern is a simple validation loop with a set or hash check. For each triplet, verify that the three characters are all different from each other. You can use a set (insert all three, check size equals three) or direct comparisons (char1 != char2 and char1 != char3 and char2 != char3). The pitfall is overthinking: some candidates try to track frequency maps across the entire input, or they assume the triplets are sorted or formatted in a specific way. The actual task is often just filtering an array or string based on the uniqueness rule. If you get stuck on edge cases (empty strings, single characters, repeated inputs) during the real OA, StealthCoder can pull the exact filtering logic and show you the clean implementation in your language of choice.
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Triplets With Unique Chars FAQ
What exactly is a 'triplet' in this problem?+
Most likely a string of exactly three characters, but check the problem statement during the OA. It could also mean an array of three elements. The key is verifying all three are unique from each other. Don't assume any ordering or format beyond the name.
How do I check if three characters are unique?+
Use a set: create a set from the three chars, check if its length is three. Or do direct comparisons: a != b and a != c and b != c. Both run in O(1) for three elements. Set is cleaner and scales if the definition ever changes.
Is this a hard problem?+
No. It's a warm-up or early screening problem. The difficulty is reading the requirement correctly and not overthinking it. If you understand the uniqueness rule, code it in under three minutes.
What if the input is very large?+
You're still checking each triplet once, so O(n) where n is the count of triplets. Space is O(1) or O(n) depending on output format. No fancy algorithm needed. Brute force is the right approach.
Should I pre-process the input or validate format?+
Assume the input is well-formed unless the problem says otherwise. Don't add defensive checks for malformed triplets unless explicitly required. Focus on the core filter logic and you're done.