Find Duplicates Among Two Lists | Dataford Interview Questions

Magic AI may compare prompt IDs collected from two product surfaces. Given two lists of integers, return the IDs that appear in both lists.

Each ID should appear at most once in the result, and the result must preserve the order in which IDs first appear in list_a. Repeated occurrences within either input list do not create repeated output values.

Formal Specification

Implement find_shared_ids(list_a, list_b).

Input: list_a and list_b, two lists of integers.
Output: A list containing every distinct integer present in both inputs, ordered by its first occurrence in list_a.
If no integer is shared, return an empty list.

Constraints

0 <= len(list_a), len(list_b) <= 100,000
-10^9 <= each list value <= 10^9
Return each shared value at most once
Preserve first-occurrence order from list_a

Function Signature

def find_shared_ids(list_a, list_b):

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