Teaching Kids Programming – Number of Unique Email Addresses

Teaching Kids Programming: Videos on Data Structures and Algorithms

Every valid email consists of a local name and a domain name, separated by the ‘@’ sign. Besides lowercase letters, the email may contain one or more ‘.’ or ‘+’.

For example, in “[email protected]”, “alice” is the local name, and “leetcode.com” is the domain name.
If you add periods ‘.’ between some characters in the local name part of an email address, mail sent there will be forwarded to the same address without dots in the local name. Note that this rule does not apply to domain names.

For example, “[email protected]” and “[email protected]” forward to the same email address.
If you add a plus ‘+’ in the local name, everything after the first plus sign will be ignored. This allows certain emails to be filtered. Note that this rule does not apply to domain names.

For example, “[email protected]” will be forwarded to “[email protected]”.
It is possible to use both of these rules at the same time.

Given an array of strings emails where we send one email to each email[i], return the number of different addresses that actually receive mails.

Example 1:
Input:

1	emails = ["[email protected]", "[email protected]", "[email protected]"]

emails = ["[email protected]", "[email protected]", "[email protected]"]

Output: 2
Explanation: “[email protected]” and “[email protected]” actually receive mails.

Example 2:
Input:

1	emails = ["[email protected]", "[email protected]", "[email protected]"]

emails = ["[email protected]", "[email protected]", "[email protected]"]

Output: 3

Constraints:
1 <= emails.length <= 100
1 <= emails[i].length <= 100
email[i] consist of lowercase English letters, ‘+’, ‘.’ and ‘@’.
Each emails[i] contains exactly one ‘@’ character.
All local and domain names are non-empty.
Local names do not start with a ‘+’ character.

Unique Email Addresses Algorithm

First, we need to obtain the account string before symbol @ and the domain after the symbol @. We can do this easily via the string.split function. Then, we can split the account string by plus sign so that we can easily strip out the label. And then we can remove the dots to remove further alias.

We push the modified/simplified email string to a set, and the result will the the length of the set.

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class Solution:
    def numUniqueEmails(self, emails: List[str]) -> int:
        def getEmail(email):
            name, domain = email.split("@")
            name = name.replace(".", "").split("+")[0]
            return name + "@" + domain
        e = set()
        for email in emails:
            e.add(getEmail(email))
        return len(e)

class Solution:
    def numUniqueEmails(self, emails: List[str]) -> int:
        def getEmail(email):
            name, domain = email.split("@")
            name = name.replace(".", "").split("+")[0]
            return name + "@" + domain
        e = set()
        for email in emails:
            e.add(getEmail(email))
        return len(e)

Time and space complexity is O(MN) where M is the length of the email addresses, and N is the average length of each email string.

See also: How to Filter the Unique Email Addresses?

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