Array Object Lookup | Dataford Interview Questions

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Problem

A Five9 contact list contains objects with an externalId field. Given the list and a target external ID, return the first contact whose externalId exactly matches the target. Return None when no contact matches.

The input list may contain duplicate external IDs. In that case, return the object with the smallest array index. Do not mutate the input list or its objects.

Formal Specification

Implement find_contact(contacts, target_external_id).

contacts is a list of objects represented as Python dictionaries. Every object contains an externalId key and may contain additional fields.
target_external_id is a string.
Return the matching dictionary itself, or None if no match exists.
Matching is case-sensitive and must use exact equality.

Constraints

0 <= len(contacts) <= 100,000
Each contact contains a string externalId
0 <= len(contact) <= 20
External IDs are case-sensitive strings of at most 100 characters

Function Signature

def find_contact(contacts, target_external_id):