Every email consists of a local name and a domain name, separated by the @ sign.
For example, in email@example.com, alice is the local name, and leetcode.com is the domain name.
Besides lowercase letters, these emails may contain ‘.’s or ‘+’s.
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. For example, “firstname.lastname@example.org” and “email@example.com” forward to the same email address. (Note that this rule does not apply for domain names.)
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, for example firstname.lastname@example.org will be forwarded to email@example.com. (Again, this rule does not apply for domain names.)
It is possible to use both of these rules at the same time.
Given a list of emails, we send one email to each address in the list. How many different addresses actually receive mails?
Explanation: “firstname.lastname@example.org” and “email@example.com” actually receive mails
1 <= emails[i].length <= 100 1 <= emails.length <= 100 Each emails[i] contains exactly one '@' character.
Time: O(N * S.Length) where N is the number of emails and S is the max length email.
Space: O(N) because N unique emails are possible for the set
Loop through all the emails and fix the local name part to remove the dots and plus sign and then combine the result with the domain name and add it to the set to get a count of all unique emails.
O(N) operations based on the length of the string.