Coding questions · Uber

Maintain the First Value That Appears Exactly Once

Practice a Uber coding interview problem focused on maintain the first value that appears exactly once. The prompt emphasizes edge cases, clean implementation, and verifiable test behavior without revealing the solution.

Design a data structure that maintains a stream of integers and returns the first value that appears exactly once.

Implement:

class FirstUniqueValue:
    def __init__(self, nums: list[int]): pass
    def show_first_unique(self) -> int: pass
    def add(self, value: int) -> None: pass

Return -1 if no value is unique.

First Unique Value in a Stream

Simulate a stream supporting add and show_first_unique operations.

Examples

Example 1

Input: {"initial":[2,3,5],"operations":[["show"],["add",5],["show"],["add",2],["show"],["add",3],["show"]]}
Output: [2,2,3,-1]

Explanation: Classic stream.

Example 2

Input: {"initial":[],"operations":[["show"]]}
Output: [-1]

Explanation: Empty.