Intersection of Two Sets | Dataford Interview Questions

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Problem

An IBM watsonx data pipeline receives two unsorted lists of integer tags. Return their intersection as a list of unique values, preserving the order in which values first appear in the first list.

Although the inputs are lists and may contain duplicates, treat each list as a mathematical set for membership. The output must contain each common value exactly once. Do not modify either input list.

Formal Specification

Implement intersection_preserving_order(nums1, nums2).

Input: Two lists of integers, nums1 and nums2.
Output: A list containing every distinct integer that occurs in both inputs, ordered by its first occurrence in nums1.
If there is no common value, return an empty list.

Constraints

0 <= len(nums1), len(nums2) <= 10^5
-10^9 <= nums1[i], nums2[i] <= 10^9
Inputs may contain repeated values
The input lists must remain unchanged

Function Signature

def intersection_preserving_order(nums1, nums2):