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Leetcode 1429. First Unique Number
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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Mid December, 2025
Uber
Mid-level
The above questions was framed in terms of Customers Visiting the website, We need to return the first One Timer.
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