Day 11 of 30 - Ruby Coding Challenge - Repdigit Number Algorithm

Hey!

This is the blog post version of the Youtube video of the Ruby Coding Challenges in 30 days.

Today we’re going to solve this simple and elegant coding challenge, which is the Repdigit Algorithm:

Given a number, I want to check if the number is composed of repeated instances of the same digit

That was the fancy definition.

Real Life:

999999

This is a Repdigit (repeated digit) because it repeats 9 for the whole number

7777

This is a Repdigit because it repeats 7 for the whole number

666664

This is not a Repdigit because it doesn’t repeat 6 for the whole number

333444777

This is not a Repdigit because it doesn’t repeat 3,4 or 7 for the whole number

I think you got it. Very simple.

#1 Repdigit Algorithm Solution

One possible solution is

• convert the number into an array
• take the first digit of the number
• check if all of the numbers are the same digit

Pretty simple, right?

Let’s see how Ruby handles it.

Step 1

The first step is actually to convert the Integer into a String so that we can be able to manipulate it

xxxxxxxxxx

array = number.to_s

Step 2

Now it’s time to create the array based on that string

xxxxxxxxxx

array = number.to_s.split('')

Step 3

Finally, let’s convert each string in the array back to an integer

xxxxxxxxxx

array = number.to_s.split('').map(&:to_i)

Step 4

I’m going to take the first digit to compare with all the numbers

xxxxxxxxxx

digit = array.first

Step 5

Then the final step is to count how many digits in that number are different from the first digit

xxxxxxxxxx

array = number.to_s.split('').map(&:to_i)

digit = array.first

count = array.count { |item| item != digit }

Perfect! If the count variable is different from zero then we have a digit that is different from the first digit, which means that the number is not Repdigit

The final solution would be:

xxxxxxxxxx

def is_repdigit(number)

  array = number.to_s.split('').map(&:to_i)

  digit = array.first

  count = array.count { |item| item != digit }

  if count == 0

    return true

  else

    return false

  end

end

puts is_repdigit(777) # true

#2 A Leaner Solution in Ruby

A little bit leaner solution would be the following:

xxxxxxxxxx

def is_repdigit_2(number)

  array = number.to_s.split('').map(&:to_i)

  array.count { |item| item != array.first } == 0

end

That’s it!

In the next video, we’re going to explore a Ruby Way to solve this algorithm. See you there :)

Don’t forget to come by and say hi Alex
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