929. Unique Email Address

1 Question

Every email consists of a local name and a domain name, seperated by the @ sign.
For example, in alice@leetcode.com, alice is teh 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, email sent there will be forwarded to teh 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 wend one email to each address in the list. How many different addresses actually receive emails?

Example:

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. 1 <= emails[i].length <= 100
• 2. 1 <= emails.length <= 100
• 3. Each emails[i] contains exactly one '@' character.

2 Solution -- Canonical Form 规范形式

For each email address, convert it to the canonical address that actually receives the email. This involves a few steps:

• seperate the email address into a local part and the rest of the address
• if the local part has a + character, remove it and everything beyond it from the local part
• remove all the zeros from the local part
• the canonical address is local + rest

After, we can count the number of unique canonical addresses with a Set structure.

class Solution(object):
    def numUniqueEmails(self, emails):
        seen = set()
        for email in emails:
            local, _, domain = email.partition('@')
            if '+' in local:
                local = local[:local.index('+')]
            seen.add(local.replace('.','') + '@' + domain)
        return len(seen)

Complexity Analysis:

• time complexity: O(C), where C is the total content of emails
• space complexity: O(C)