8. Unique Email Addresses

Title：

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

For example, in alice@leetcode.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, "alice.z@leetcode.com" and "alicez@leetcode.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 m.y+name@email.com will be forwarded to my@email.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? 

Example 1:

Input: ["test.email+alex@leetcode.com","test.e.mail+bob.cathy@leetcode.com","testemail+david@lee.tcode.com"]
Output: 2
Explanation: "testemail@leetcode.com" and "testemail@lee.tcode.com" actually receive mails

Note:

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

Analysis of Title：

Be aware the twice of 'node':this rule does not apply for domain names.

So we need to split the domain and the local name.

The train of thought is 

1. Spilt the add to local name and domain.

2.Go through the local then get the str without dots and ignoted everything after the first plus sign.

3.Append the local name after being processed add domain.

4.Finally to de-duplication we set the result in the 'set'.

Test case：

["test.email+alex@leetcode.com","test.e.mail+bob.cathy@leetcode.com","testemail+david@lee.tcode.com"]

Python：

class Solution:
　　def numUniqueEmails(self, emails):
　　"""
　　:type emails: List[str]
　　:rtype: int
　　"""
　　email_set = set()
　　for email in emails:
　　　　name, domain = email.split('@')   #!!!! Learning this method that I didn't not before.
　　　　name = name[:name.find('+')].replace('.', '') #!!!注意从后往前执行，若将切片放在后面，则输出 #['testemail+', 'testemail+b', 'testemail']
　　　　email_set.add(name + '@' + domain)
　　return len(email_set)

Analysis of Code：

Those all was in the analysis of title.