Hey friends!

This is the blog post version of the Youtube video from the 30 Ruby Coding Challenges in 30 Days series

Let’s go straight to the point

Coding Challenge

Create a function that takes an array of numbers between 1 and 10 (excluding one number) and returns the missing number.

A few points:

• The array of numbers will be unsorted (not in order).
• Only one number will be missing.

Examples

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find_missing_num([1, 2, 3, 4, 6, 7, 8, 9, 10]) ➞ 5

find_missing_num([7, 2, 3, 6, 5, 9, 1, 4, 8]) ➞ 10

find_missing_num([10, 5, 1, 2, 4, 6, 8, 3, 9]) ➞ 7

Pretty simple, isn’t it?

Algorithm in Ruby

Let’s break the algorithm down to a few small steps:

Step 1

We need to go through a list of items (an array), going from 1 to 10.

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def find_missing_num(array)

  [1, 2, 3, 4, 5, 6, 7, 8, 9, 10].each do |item|

    end

end

array = [1, 2, 3, 4, 6, 7, 8, 9, 10]

find_missing_num(array)

Ruby provides us a really better way to do this:

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def find_missing_num(array)

  (1..10).each do |item|

    end

end

array = [1, 2, 3, 4, 6, 7, 8, 9, 10]

find_missing_num(array)

Step 2

We’re going to compare each number (from 1 to 10) with the numbers in the given array.

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def find_missing_num(array)

  (1..10).each do |item|

    array.each do |number|

      if item == number

        break # breaking the execution

      end      

    end

  end

end

array = [1, 2, 3, 4, 6, 7, 8, 9, 10]

find_missing_num(array)

We break the execution once if find the desired number because we don’t need to continue looking for the number

Step 3

Because we want to return the number that wasn’t found in the array, I’m going to create a local variable to indicate that.

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def find_missing_num(array)

  (1..10).each do |item|

    found = false

    array.each do |number|

      if item == number

        found = true

        break

      end      

    end

    if found = false

      return item

    end

  end

end

array = [1, 2, 3, 4, 6, 7, 8, 9, 10]

find_missing_num(array)

That’s it!

I know, that’s not beautiful but it works : )

Do you have a better/different version? Drop that in the comments and bring more healthy discussions :)

Thanks for the visit and in the next coding challenge we’re going to explore a more decent way to solve this puzzle, see you there!

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