[每日 LeetCode] 929. Unique Email Addresses

原文链接 [每日 LeetCode] 929. Unique Email Addresses

Description:

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.
• All local and domain names are non-empty.
• Local names do not start with a '+' character.

思路：本题要求判断字符串数组中邮箱地址的唯一性。需要注意的是 . 和 + 的特殊意义，可以遍历 emails 中的每个邮箱地址，然后依次进行如下操作：

• 分别保存数组元素中的用户名和域名；
• 从前往后遍历用户名的每个字符，如果遇到'+'，则直接截断；如果遇到'.'，则忽略该字符；
• 将新用户名和域名重新组合，再插入哈希表中
  最终哈希表的大小就是答案。

C++ 代码

class Solution {
public:
    int numUniqueEmails(vector<string>& emails) {
        unordered_set<string> S;
        for (auto email : emails)
        {
            string local, domain;
            int k = 0;
            while (email[k] != '@') k ++ ;
            local = email.substr(0, k);
            domain = email.substr(k + 1);
            string newLocal;
            for (auto c : local)
            {
                if (c == '+') break;
                if (c != '.') newLocal += c;
            }
            S.insert(newLocal + '@' + domain);
        }
        return S.size();
    }
};

运行时间：32ms

运行内存：14.4M