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Implement two-pointer unique-pair sum search

CitadelData Scientist · Technical Screen
MediumData ScientistTechnical ScreenCoding & Algorithms

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Implement two-pointer unique-pair sum search evaluates algorithm design, data structures, correctness, complexity, edge cases, and implementation details in a realistic interview setting. A strong answer states assumptions, handles edge cases, explains trade-offs, and shows how to validate the result clearly.

Given a nondecreasing integer array nums and an integer target, return all unique value pairs [a, b] with a <= b such that a + b == target. Use the two-pointer technique to achieve O(n) time and O(

  1. extra space beyond the output, and ensure duplicates in nums do not produce duplicate pairs. Additionally: a) Describe how you would return indices instead of values and any implications for stability. b) Explain how you would adapt the method if nums arrives as a stream that cannot be fully stored in memory. c) Analyze time and space complexity.