929. Unique Email Addresses

題目敘述

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.

Example 1:

Input: emails = ["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.

Example 2:

Input: emails = ["a@leetcode.com","b@leetcode.com","c@leetcode.com"]
Output: 3

Constraints:

• 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.

題目翻譯

此題目會給一個陣列，其中的元素都是 Email 的資料。以 @ 為區別，前面是 local name 後面是 domain name。在 local name 的部分有兩個條件。當包含 . 的部分會忽略，例如 a.b 相當於 ab。而當包含 + 的時候，會忽略連接的字，例如 a+b 相當於 a。而在這兩個條件的情況下，要去判斷有幾個不重複的 Email。

解法解析

這題的解法是很簡單的，使用一個迴圈基本上就可以處理。Time complexity：O(n)，Space complexity：O(1)。 這題主要 focus 在迴圈中處理 local name 的條件判斷，清除 . 或 + 之後跟 domain name 重組回 email，後直接存在 Set 中做去重的處理。最後判斷 Set 的大小就可以了。

程式範例

Python

class Solution:
    def numUniqueEmails(self, emails: List[str]) -> int:
        seen = set()
        for email in emails:
            name, domain = email.split('@')
            local = name.split('+')[0].replace('.', '')
            seen.add(f'{local}@{domain}')
        return len(seen)

JavaScript

/**
 * @param {string[]} emails
 * @return {number}
 */
var numUniqueEmails = function(emails) {
    return new Set(
        emails.map(
            (mail) =>
                `${mail.split('@')[0].replace(/\+.*$|\./g, '')}@${
                    mail.split('@')[1]
                }`
        )
    ).size;
};

Go

func numUniqueEmails(emails []string) int {
    m := map[string]bool{}
    for _, e := range emails {
        a := strings.Split(e, "@")
        l := strings.Split(a[0], "+")[0]
        l = strings.ReplaceAll(l, ".", "")
        m[fmt.Sprintf("%s@%s", l, a[1])] = true
    }
    return len(m)
}

Swift

class Solution {
    func numUniqueEmails(_ emails: [String]) -> Int {
        guard emails.count > 0 else { return 0 }
        var resultSet = Set<String>()

        for email in emails {
            let seperated = email.split(separator: "@")
            let local = seperated[0], validDomain = seperated[1]
            var validLocal = String()

            for char in local where char != "." {
                guard char != "+" else { break }
                validLocal.append(char)
            }

            let validFormat = validLocal + "@" + validDomain
            resultSet.insert(String(validFormat))
        }
        return resultSet.count
    }
}

Kotlin

class Solution {
    fun numUniqueEmails(emails: Array<String>): Int {
        return emails
                .map {
                    val localName =
                            it.substringBefore('@').filter { c -> c != '.' }.substringBefore('+')
                    val address = it.substringAfter('@')
                    "$localName@$address"
                }
                .toSet()
                .size
    }
}