Find Valid Emails Python solution

Use pandas: filter the DataFrame with df[df['email'].str.match(r'^[A-Za-z][A-Za-z0-9_.-]*@leetcode\\.com$')] and then select user_id and email, sorted by user_id. The regex enforces the prefix rules and the exact domain in one step.

Is Find Valid Emails easy or hard?

The problem is rated Easy with a 44.1 percent acceptance rate. The core challenge is writing a correct regex that enforces the prefix start rule and the exact domain. Once the pattern is clear, the query is a single WHERE clause.

How to solve Find Valid Emails in O(n)?

Treat each row as a constant-time check when emails are short, then apply a single regex filter across the table. The regex engine reads each character once per row, so the work scales linearly with the number of rows. Finish by ordering the result by user_id.

What is the best approach for Find Valid Emails?

The best approach is a regular expression that matches the full email in one pass. Use the pattern ^[A-Za-z][A-Za-z0-9_.-]*@leetcode\\.com$ with REGEXP in MySQL or str.match in Pandas. The anchors ensure the entire string matches, not just a substring.

What data structure is used in Find Valid Emails?

No dedicated data structure is needed. The solution works on a table of rows and relies on the regex engine's finite automaton to match each email string. You only need the Users table and a filter clause.

What is the time complexity of Find Valid Emails?

The time complexity is O(n * L), where n is the number of rows and L is the average email length. Each email is scanned once by the pattern engine. The extra space is O(1) beyond the output.

Is Find Valid Emails asked at Google, Amazon, or Meta?

The problem is tagged Database on FleetCode, but company-specific frequency data is not included in the tags. Practice SQL pattern matching and string filtering, since these topics appear across many database interview rounds.

Description Solution Video 5:56

3436. Find Valid Emails

Easy44.1% acceptance

Table: Users

+-----------------+---------+
| Column Name     | Type    |
+-----------------+---------+
| user_id         | int     |
| email           | varchar |
+-----------------+---------+
(user_id) is the unique key for this table.
Each row contains a user's unique ID and email address.

Write a solution to find all the valid email addresses. A valid email address meets the following criteria:

It contains exactly one @ symbol.
It ends with .com.
The part before the @ symbol contains only alphanumeric characters and underscores.
The part after the @ symbol and before .com contains a domain name that contains only letters.

Return the result table ordered by user_id in ascending order.

Example:

Input:

Users table:

+---------+---------------------+
| user_id | email               |
+---------+---------------------+
| 1       | alice@example.com   |
| 2       | bob_at_example.com  |
| 3       | charlie@example.net |
| 4       | david@domain.com    |
| 5       | eve@invalid         |
+---------+---------------------+

Output:

+---------+-------------------+
| user_id | email             |
+---------+-------------------+
| 1       | alice@example.com |
| 4       | david@domain.com  |
+---------+-------------------+

Explanation:

alice@example.com is valid because it contains one @, alice is alphanumeric, and example.com starts with a letter and ends with .com.
bob_at_example.com is invalid because it contains an underscore instead of an @.
charlie@example.net is invalid because the domain does not end with .com.
david@domain.com is valid because it meets all criteria.
eve@invalid is invalid because the domain does not end with .com.

Result table is ordered by user_id in ascending order.

Topics

Database

5:56

Still stuck?Read the written solution, or watch a walkthrough.

Open solution

LanguageLoading editor…

1# Write your MySQL query statement below

Starter codeMySQLSpaces: 4

Examples

Case 1

Input

{"headers":{"Users":["user_id","email"]},"rows":{"Users":[[1,"alice@example.com"],[2,"bob_at_example.com"],[3,"charlie@example.net"],[4,"david@domain.com"],[5,"eve@invalid"]]}}

Your code is saved on this device.Solution