Number of Unique Good Subsequences
A hard-tier problem at 52% community acceptance, tagged with String, Dynamic Programming. Reported in interviews at Oracle and 0 others.
You're staring at a subsequence counting problem with a twist: the word 'good' hides the real constraint. This one lands at Hard, but the acceptance rate sits at 52%, which means half the people who attempt it solve it and half don't. Oracle has asked it. The trap is simple: without understanding the deduplication rule baked into 'good', you'll either double-count or miss entire valid answers. If this problem hits your live assessment and the trick doesn't click immediately, StealthCoder surfaces a working solution in seconds, invisible to the proctor.
Companies that ask "Number of Unique Good Subsequences"
Number of Unique Good Subsequences 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 because the OA filter rejects engineers who'd pass the on-site. That's a broken filter. This is the workaround.
Get StealthCoderThe core challenge is that you can't naively count all subsequences using DP because 'good' has a specific meaning: no leading zeros. That constraint forces you to track state in a way that normal subsequence-counting solutions miss. You need dynamic programming, sure, but the state transition isn't just 'include this character or don't'. You're building a string via subsequence and rejecting any path that starts with zero. The wrong approach treats it like a standard DP digit DP or substring problem and loses points to edge cases. Most candidates either implement it without the zero-check or bloat the state space unnecessarily. If you've never seen the pattern, that's where the problem bites. StealthCoder handles the state design and pruning logic so you don't tank on submission.
Pattern tags
You know the problem.
Make sure you actually pass it.
Number of Unique Good Subsequences 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 because the OA filter rejects engineers who'd pass the on-site. That's a broken filter. This is the workaround. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Number of Unique Good Subsequences interview FAQ
How hard is this really, given the 52% acceptance rate?+
52% means it's genuinely difficult, but not impossible. You likely need to recognize the subsequence DP pattern and add the 'good' constraint (no leading zeros) correctly. If you've drilled standard DP problems but haven't hit this exact variant, you can get stuck on the state design.
Do I need to know a special technique for this?+
Not a secret technique, but you do need to think about state carefully. Most candidates know DP. The hard part is realizing you must track whether your current subsequence has started, and reject strings that begin with zero. That's the pattern.
Is this still asked at FAANG level companies?+
Oracle has reported asking it. It's in the Hard tier and tests DP mastery plus constraint modeling. Expect it at technical companies that care about dynamic programming rigor.
What's the most common mistake?+
Treating it like a standard 'count subsequences' problem without the leading-zero constraint. You end up counting invalid sequences. The second trap is overcomplicated state tracking that makes the DP slow or memory-heavy.
How does this relate to other string and DP topics?+
It sits at the intersection. You're doing DP on a string, similar to subsequence problems, but adding a constraint that feels like digit DP (where leading zeros matter). If you've solved both, the pattern should click faster.
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