Unique Email Groups - Solution & Explanation

You are given an array of strings emails, where each string is a valid email address.

Two email addresses belong to the same group if both their normalized local names and normalized domain names are identical.

The normalization rules are as follows:

• The local name is the part before the '@' symbol.
  • Ignore all dots '.'.
  • Ignore everything after the first '+', if present.
  • Convert to lowercase.
• The domain name is the part after the '@' symbol.
  • Convert to lowercase.

Return an integer denoting the number of unique email groups after normalization.

 

Example 1:

Email	Local	Normalized Local	Domain	Normalized Domain	Final Email
test.email+alex@leetcode.com	test.email+alex	testemail	leetcode.com	leetcode.com	testemail@leetcode.com
test.e.mail+bob.cathy@leetcode.com	test.e.mail+bob.cathy	testemail	leetcode.com	leetcode.com	testemail@leetcode.com
testemail+david@lee.tcode.com	testemail+david	testemail	lee.tcode.com	lee.tcode.com	testemail@lee.tcode.com

Unique emails are ["testemail@leetcode.com", "testemail@lee.tcode.com"]. Thus, the answer is 2.

Example 2:

Example 3:

 

Constraints:

• 1 <= emails.length <= 1000
• 1 <= emails[i].length <= 100
• emails[i] consists of lowercase and uppercase English letters, digits, and the characters '.', '+', and '@'.
• Each emails[i] contains exactly one '@' character.
• All local and domain names are non-empty; local names do not start with '+'.
• Domain names end with the ".com" suffix and contain at least one character before ".com".