Highest Value Palindrome

Welcome to the Ruby challenge. Fork the repository and submit your solution as a pull request.

Task

You are to develop the function highest_value_palindrome located at lib/highest_value_palindrome.rb so that when given an input string and a maximum number of changes it returns the highest value palindrome. A palindrome is a string which reads the same from both sides. The highest value describes the value the palindrome would represent if it was converted to an integer. Changing the value of a single digit in the number is considered a change. I.e. turning 1234 into 1256 "used" two changes.

Function description

The function has two input parameters: input_string and number_of_changes. The first is a string made up of numbers from 0 to 9. The second one describes the maximum number of changes required to turn said string into the highest value palindrome possible. If no polindrome is possible the ouput of the function should be nil. Leading 0's count as normal numbers and the length of the ouput string must match the length of the input string.

For uncertainties or questions please open an issue. Contributions via pull request are also welcome!

To verify your implementation please run the tests.

Examples

highest_value_palindrome(3943, 1) # => 3993
highest_value_palindrome(092282, 3) # => 992299
highest_value_palindrome(0011, 1) # => nil

For more examples have a look at the tests.

Constraints

• Only built in gems and functions are to be used.
• Only highest_value_palindrome.rb is subject to change.
• If you want to add more tests feel free but the existing ones must stay.

Setup

• Install Ruby 2.7.3
• Install bundler (gem install bundler)
• Setup project:

git clone https://github.com/renuo/highest-value-palindrome.git
cd highest-value-palindrome
bin/setup

Tests

bin/check

Credits

• https://www.hackerrank.com/challenges/richie-rich/problem
• https://medium.com/@lonell.liburd/highest-value-palindrome-1275edcd1430