Practice: Area Codes#

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Write a function called area_codes that takes a list of str as input where each str in the list is a phone number and returns the number of unique area codes found in those phone numbers. Each phone number will be of the format '123-456-7890' and the area code is the first three characters in the str .

For example, if we were to call

area_codes([
    '123-456-7890',
    '206-123-45676',
    '123-000-0000',
    '425-999-9999'
])

This call would return 3 because there are 3 unique area-codes in these phone numbers ( 123 , 206 , 425 ).

You may assume that each str in the list is a valid phone number. However, you should not assume anything about the number of elements in the list .

Hint: Try solving an easier version of this problem that just prints all the area codes for the provided phone numbers.

Requirements#

  • Your solution should use a structure that can solve this problem efficiently, even if there are a large number of phone numbers