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Find Users With Valid E-Mails Problem

EasyUpdated: Sep 26, 2024
Practice on:
LeetCode

Problem

Table: Users

+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| user_id       | int     |
| name          | varchar |
| mail          | varchar |
+---------------+---------+

user_id is the primary key (column with unique values) for this table. This table contains information of the users signed up in a website. Some e-mails are invalid.

Write a solution to find the users who have valid emails.

A valid e-mail has a prefix name and a domain where:

  • The prefix name is a string that may contain letters (upper or lower case), digits, underscore '_', period '.', and/or dash '-'. The prefix name must start with a letter.
  • The domain is '@leetcode.com'.

Return the result table in any order.

The result format is in the following example.

Examples

Example 1:

Input: Users table:

+---------+-----------+-------------------------+
| user_id | name      | mail                    |
+---------+-----------+-------------------------+
| 1       | Winston   | [email protected]    |
| 2       | Jonathan  | jonathanisgreat         |
| 3       | Annabelle | [email protected]     |
| 4       | Sally     | [email protected] |
| 5       | Marwan    | quarz#[email protected] |
| 6       | David     | [email protected]       |
| 7       | Shapiro   | [email protected]     |
+---------+-----------+-------------------------+

Output:

+---------+-----------+-------------------------+
| user_id | name      | mail                    |
+---------+-----------+-------------------------+
| 1       | Winston   | [email protected]    |
| 3       | Annabelle | [email protected]     |
| 4       | Sally     | [email protected] |
+---------+-----------+-------------------------+

Explanation: The mail of user 2 does not have a domain. The mail of user 5 has the # sign which is not allowed. The mail of user 6 does not have the leetcode domain. The mail of user 7 starts with a period.

Solution

Method 1 - Using Regexp

Code

A detailed explanation of the following regular expression solution:

'^[A-Za-z]+[A-Za-z0-9\_\.\-]*@leetcode.com'

  1. ^ means the beginning of the string
  2. [] means character set. [A-Z] means any upper case chars. In other words, the short dash in the character set means range.
  3. After the first and the second character set, there is a notation: + or * - + means at least one of the character from the preceding charset, and * means 0 or more.
  4. \ inside the charset mean skipping. In other words, \. means we want the dot as it is. Remember, for example, - means range in the character set. So what if we would like to find - itself as a character? use \-.
  5. Everything else, like @leetcode.com refers to exact match.
SQL
select * from Users 
where regexp_like(mail, '^[A-Za-z]+[A-Za-z0-9\_\.\-]*@leetcode.com')
Pandas
import pandas as pd

def valid_emails(users: pd.DataFrame) -> pd.DataFrame:
  return users[
    users['mail'].str.match(r'^[a-zA-Z][a-zA-Z\d_.-]*@leetcode\.com')
  ]

Complexity

  • Time: O(b)
  • Space: O(1)

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