Every email consists of a local name and a domain name, separated by the @ sign.

For example, in [email protected], 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, "[email protected]" and "[email protected]" 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 [email protected] will be forwarded to [email protected].  (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? 

 

Example 1:

Input: ["[email protected]","[email protected]","[email protected]"]
Output: 2
Explanation: "[email protected]" and "[email protected]" actually receive mails

 

Note:

• 1 <= emails[i].length <= 100
• 1 <= emails.length <= 100
• Each emails[i] contains exactly one '@' character.

 

 

 

 

 

split()的用法

    public int numUniqueEmails(String[] emails) {
        Set<String> normalized = new HashSet<>();
        for (String email : emails) {
            String[] parts = email.split("@"); // split into local and domain parts.
            String[] local = parts[0].split("\\+"); // split local by '+'.
            normalized.add(local[0].replace(".", "") + "@" + parts[1]); // remove all '.', and concatenate '@' and domain.        
        }
        return normalized.size();
    }

reference：https://leetcode.com/problems/unique-email-addresses/discuss/186798/Java-7-liner-with-comment.