Multiply all even indexed integers by two

Question

Wanting to take a fixnum of integers and multiply all even(indexed) integers by two. I figured the best way to do this is first turn fixnum into an array. So lets say the following number of 16 digits: a = 4408041234567901

I know I could:

a.to_s.split('')

Which will return 'a' to an array of 'stringed' numbers. But then I cant follow up with:

a.map!.with_index {|i,n| i.even? n*2}

Guess I'm kinda stuck on how to create a method to do this. So my question may even be how to turn that group of numbers into an array of fixnums/integers instead of strings.

Answer 1

To change it to an Array, you could do

a = 4408041234567901
arr = a.to_s.chars.map(&:to_i)
# => [4, 4, 0, 8, 0, 4, 1, 2, 3, 4, 5, 6, 7, 9, 0, 1]

You can also multiply alternate numbers by 2

arr = a.to_s.chars.map.with_index {|n,i| i.even? ? n.to_i * 2 : n.to_i }
# => [8, 4, 0, 8, 0, 4, 2, 2, 6, 4, 10, 6, 14, 9, 0, 1]

Improving a little bit, you can use a Hash to find the number to be multiplied.

h = {true => 2, false => 1}
a.to_s.each_char.map.with_index {|n,i| n.to_i * h[i.even?]}

EDIT

I can explain each step, But it will be better if you can try to figure it out on your own. Open irb, type a.to_s and check the output. Then type a.to_s.chars and inspect the output and so on..