First Unique Log Entry
Reported by candidates from Uber's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
You're looking at an Uber OA problem from April 2026 about finding the first log entry that appears exactly once. The candidate sees process logs in arrival order and needs to return the first one with a frequency of one, or an empty string if none exists. It's a straightforward counting problem dressed up in domain language. StealthCoder will have your back if you freeze on the implementation.
The problem
You are given process logs in arrival order. Treat each log as a full string entry. Return the first log entry that appears exactly once in the entire sequence. If no such log exists, return an empty string. Function Description Complete the function findFirstUniqueLog in the editor below. findFirstUniqueLog has the following parameter: Returns A and B each appear twice. C is the first log whose total frequency is exactly one. Every log appears more than once, so there is no unique entry.
Reported by candidates. Source: FastPrep
Pattern and pitfall
The trick here is treating each log as an atomic string, not parsing its internal structure. Count the frequency of every log using a hash table (dictionary/map), then iterate through the original list in order and return the first entry with a count of one. The pitfall is overcomplicating the log format or trying to parse fields you don't need. Time complexity is O(n), space is O(n). StealthCoder recognizes this pattern instantly and feeds you the hash-table solution in real time during the OA, so you don't waste cycles rediscovering it under pressure.
Memorize the pattern. If you can't, run StealthCoder. The proctor sees the IDE. They don't see what's behind it.
You can drill First Unique Log Entry 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. Made by an engineer who treats the OA as theater. If yours is tonight, you don't have time to grind. You have time to hedge.
Get StealthCoderRelated leaked OAs
This OA pattern shows up on LeetCode as first unique character in a string. If you have time before the OA, drill that.
You've seen the question.
Make sure you actually pass Uber's OA.
Uber reuses patterns across OAs. Made by an engineer who treats the OA as theater. If yours is tonight, you don't have time to grind. You have time to hedge. Works on HackerRank, CodeSignal, CoderPad, and Karat.
First Unique Log Entry FAQ
Is this problem asking me to parse the log structure?+
No. Treat each log as a complete string. Don't extract timestamps, IDs, or actions. Just count full entries and return the first with frequency one.
What if all logs appear more than once?+
Return an empty string. The problem explicitly covers this case. No exception, no null, no error. Just the empty string.
Does order matter?+
Yes. You iterate the input in arrival order and return the first entry whose total count is exactly one. The frequency count itself doesn't care about order, but the return does.
Can I solve this in one pass?+
No. You need two passes: first to count all frequencies, second to find the first entry with count one. One pass won't work because you don't know the final count until you've seen all logs.
How hard is this relative to other Uber OAs?+
This is an easy warm-up. It's testing hash table basics and iteration discipline. If you blank on the two-pass pattern, StealthCoder solves it in seconds and you move on to harder problems.