Unique Email Addresses

🔗 문제 링크

https://leetcode.com/problems/unique-email-addresses/

❔ 문제 설명

Every valid email consists of a local name and a domain name, separated by the '@' sign. Besides lowercase letters, the email may contain one or more '.' or '+'.

For example, in "alice@leetcode.com", "alice" is the local name, and "leetcode.com" is the domain name.

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. Note that this rule does not apply to domain names.

For example, "alice.z@leetcode.com" and "alicez@leetcode.com" forward to the same email address.

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. Note that this rule does not apply to domain names.

For example, "m.y+name@email.com" will be forwarded to "my@email.com".

It is possible to use both of these rules at the same time.

Given an array of strings emails where we send one email to each email[i], return the number of different addresses that actually receive mails.

⚠️ 제한사항

• 1 <= emails.length <= 100

• 1 <= emails[i].length <= 100

• email[i] consist of lowercase English letters, '+', '.' and '@'.

• Each emails[i] contains exactly one '@' character.

• All local and domain names are non-empty.

• Local names do not start with a '+' character.

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💡 풀이 (언어 : Java)

@기준으로 두개로 나누고 오른쪽 도메인 이름은 별다른 처리가 필요없다. 왼쪽의 로컬 이름은 정규식으로 '.'과 +로 시작하는 단어를 삭제해준다. 그리고 @와 함께 StringBuiluder로 합친 후 String으로 변환한다. 이것을 HashSet에 넣어주어 중복을 제거해주고, 마지막에 이것의 사이즈를 체크하면 정답이다.

class Solution {
    public int numUniqueEmails(String[] emails) {
        HashSet<String> set = new HashSet<>();
        for (String em: emails) {
            String[] localDomain = em.split("@");
            StringBuilder sb = new StringBuilder();
            set.add(sb.append(localDomain[0].replaceAll("\\.|[+].*", ""))
                    .append("@").append(localDomain[1]).toString());
        }
        return set.size();
    }
}