929. Unique Email Addresses

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 ('.'

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.

題目描述：大概是給你個郵箱的列表，給了一個 local name 的命名規則，問如果同時向這些郵箱中傳送郵件，有多少不同郵箱能夠實際收到這些郵件。

題目分析：挺水的一道題，首先，郵箱是由local name + @ + domain name 組成。我們從題意可以知道給出 local name 的兩條命名規則：

• 遇到 . 直接無視。例如 [email protected] 和 [email protected] 是等價的關係
• 遇到 + ，忽略 + 後面的內容。例如 [email protected] 和 [email protected] 是等價的關係

我們考慮用集合進行去重操作，同一郵箱收到多條郵件只能算做一次。列舉郵箱列表中的郵箱地址，根據 local name 的命名規則，通過 split 函式分割，將真實郵箱存入集合中，然後計算出的集合中的元素個數即為我們所求的郵箱數。

python 程式碼：

class Solution(object):
    def numUniqueEmails(self, emails):
        """
        :type emails: List[str]
        :rtype: int
        """
        real_email = set()
        for i in range(len(emails)):
            x = emails[i]
            s = str(x.split("+")[0].replace('.','') + '@' + x.split("@")[1])
            real_email.add(s)
        
        return len(real_email)

C++ 程式碼：

class Solution {
public:
    int numUniqueEmails(vector<string>& emails) {
        set<string> x;
        for(int i = 0; i < emails.size(); i++){
            if(emails[i].find('.') != string::npos){
                emails[i].erase(remove(emails[i].begin(), find(emails[i].begin(), emails[i].end(),'@'), '.'), find(emails[i].begin(), emails[i].end(), '@'));
            }
            if(emails[i].find('+') != string::npos){
                emails[i].erase(find(emails[i].begin(), find(emails[i].begin(), emails[i].end(), '@'), '+'), find(emails[i].begin(), emails[i].end(), '@'));
            }
            x.insert(emails[i]);
        }
        return x.size();
    }
};