Available question text
Design a data structure that, given an initial list and a stream of added numbers, returns the first integer that appears exactly once at any time. The core challenge is maintaining element frequencies while preserving insertion order so queries for the current first unique remain efficient.
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Sources · 2 references
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Hello Interview · 1 record
Uber
Leetcode 1429. First Unique Number
Reported Jun 1, 2026 · 20 source reports
MID_LEVEL, SENIOR, STAFF
Source snapshot: Nov 12, 2026
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LeetCode company tags · 1 record
Uber
First Unique Number
Reported date not specified · Source window: 6mo
Source snapshot: Oct 20, 2026
Source frequency score: 100. This is not an interview probability.
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