Reviewed by Aditya Kumar · Last reviewed 2026-03-24
To find the number of unique pairs that sum up to a target, an efficient approach involves using a hash set (or set in Python) to keep track of numbers encountered. This allows for O(1) average case…
This easy-level Python/Coding question appears frequently in data engineering interviews at companies like Amazon. While less common, it tests deeper understanding that distinguishes strong candidates. Mastering the underlying concepts (python) will help you answer variations of this question confidently.
Start by clearly defining the core concept being asked about. Interviewers want to see that you understand the fundamentals before diving into implementation details. Structure your answer with a definition, then explain the practical application with a concise example.
To find the number of unique pairs that sum up to a target, an efficient approach involves using a hash set (or set in Python) to keep track of numbers encountered. This allows for O(1) average-case lookup time, leading to an overall O(N) time complexity.
The core idea is to iterate through the list once. For each number x, we calculate its complement (which is target - x). If this complement has been seen before, we've found a pair. To ensure we count unique value pairs (e.g., (1, 5) is one pair, not two if (5, 1) is also found, and `(3,
Pro-Move: Handle duplicate pairs. Red Flag: Double-counting.
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According to DataEngPrep.tech, this is one of the most frequently asked Python/Coding interview questions, reported at 1 company. DataEngPrep.tech maintains an editor-reviewed database of 1,863 data engineering interview questions across 7 categories.