Alien Username – HackerRank Solution

In this post, we will solve Alien Username HackerRank Solution. This problem (Alien Username) is a part of HackerRank Regex series.


In a galaxy far, far away, on a planet different from ours, each computer username uses the following format:

  1. It must begin with either an underscore, _ (ASCII value 95), or a period, . (ASCII value 46).
  2. The first character must be immediately followed by one or more digits in the range 0 through 9.
  3. After some number of digits, there must be 0 or more English letters (uppercase and/or lowercase).
  4. It may be terminated with an optional _ (ASCII value 95). Note that if it’s not terminated with an underscore, then there should be no characters after the sequence of 0 or more English letters.

Given n strings, determine which ones are valid alien usernames. If a string is a valid alien username, print VALID on a new line; otherwise, print INVALID.

Input Format

The first line contains a single integer, n, denoting the number of usernames.
Each line i of the n subsequent lines contains a string denoting an alien username to validate.


  • 1 <= n <= 100

Output Format

Iterate through each of the n strings in order and determine whether or not each string is a valid alien username. If a username is a valid alien username, print VALID on a new line; otherwise, print INVALID.

Sample Input


Sample Output



We validate the following three usernames:

  1. _0898989811abced_ is valid as it satisfies the requirements specified above. Thus, we print VALID.
  2. _abce is invalid as the beginning _ is not followed by one or more digits. Thus, we print INVALID.
  3. _09090909abcD0 is invalid as the sequence of English alphabetic letters is immediately followed by a number. Thus, we print INVALID.

Solution – Alien Username – HackerRank Solution


import re
pattern = re.compile('^[_\.][0-9]+[a-zA-Z]*[_]?$')
n = int(input())
for i in range(n):
    x = str(input())
    if(len(re.findall(pattern,x)) != 0):

Note: This problem (Alien Username) is generated by HackerRank but the solution is provided by CodingBroz. This tutorial is only for Educational and Learning purpose.

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