Longest Common Prefix of Number Pairs
Reported by candidates from DataBricks's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
DataBricks hit you with Longest Common Prefix of Number Pairs in September 2024, and it looks like a string problem but lives in the space between strings and numbers. You're comparing numeric values as strings, finding the longest prefix they share. The trick is that you can't just treat this as a character-by-character string comparison without understanding what "number pairs" means in the context of the OA. StealthCoder will catch the problem statement nuance in real time if you zone out.
Pattern and pitfall
This is fundamentally a prefix-matching problem that can be solved greedily (compare characters left to right until mismatch) or with dynamic programming if the problem adds constraints like multiple number pairs or weighted scoring. The greedy approach is O(n*m) where n is the number of pairs and m is the length of the shortest number. The DP angle probably emerges if you need to optimize for repeated subproblems or handle a larger dataset. The pitfall: treating the numbers as integers and losing leading zeros, or overthinking memoization when a two-pointer scan solves it. StealthCoder is your safety net if the problem statement is ambiguous on the OA platform itself.
If you see this problem in your OA tomorrow, the play is to recognize the pattern in 30 seconds. StealthCoder buys you that recognition.
You can drill Longest Common Prefix of Number Pairs cold, or you can hedge it. StealthCoder runs invisibly during screen share and surfaces a working solution in under 2 seconds. The proctor sees the IDE. They don't see what's behind it. Built by an Amazon engineer who passed his OA cold and still thinks the filter is broken.
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This OA pattern shows up on LeetCode as longest common prefix. If you have time before the OA, drill that.
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DataBricks reuses patterns across OAs. Built by an Amazon engineer who passed his OA cold and still thinks the filter is broken. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Longest Common Prefix of Number Pairs FAQ
Is this actually a DP problem or can I solve it greedily?+
Greedy works for the core logic: scan both strings left to right, stop at the first mismatch. DP hints suggest the real OA may add constraints like finding the longest common prefix across all pairs simultaneously, or optimizing for repeated queries. Greedy is your baseline.
Do I need to handle leading zeros in numbers?+
Yes. Treat the numbers as strings to preserve leading zeros. Converting to integers will corrupt them. This is a common trick in DataBricks OAs that catch candidates who optimize too early.
What's the time complexity I should aim for?+
O(n*m) where n is the number of pairs and m is the minimum length of any pair. That's two-pointer scans. If DataBricks asks for better, they want DP or a trie, but that's unlikely without explicit constraints.
Should I preprocess the pairs or compare them on the fly?+
On the fly is cleaner. Sort the pairs first if length matters, or just iterate. Preprocessing gains you nothing unless the OA explicitly asks for multiple queries on the same dataset.
How do I prepare for this in 48 hours if I've never seen it?+
Understand two-pointer prefix matching first. Code it clean once. Then think about edge cases: single pair, all identical pairs, completely different pairs, empty input. That's your OA coverage.