The reason I do codewars is to see other people's answers after I complete a challenge as it helps me learn. Clearly have a lot to learn!

Me too, I'm very confused. Did you figure it out?

In the test, sometimes the expected isbn is in this format 000-0-00000-000-0 and sometimes it is in this format: 000-0-00-000000-0 and sometimes in this format: 000-000-00-0000-0

all of my isbns are returned in the first format so I'm failing th tests. HOw do I know which format to use for which ISBNs?

Oh I think I answered the question, because the dashes need to be in the same place as they are in the original? I was confused because I thought that ISBNs are always in the format of the first example in the tests above. I will have another go.

why are the test output ISBNs in different formats - with dashes at different places? It doesn't mention this in the output instructions.

describe "Sample tests" do
  it "Some examples" do
    expect(isbn_converter("1-85326-158-0")).to eq("978-1-85326-158-9")
    expect(isbn_converter("0-14-143951-3")).to eq("978-0-14-143951-8")
    expect(isbn_converter("0-02-346450-X")).to eq("978-0-02-346450-8")
    expect(isbn_converter("963-14-2164-3")).to eq("978-963-14-2164-4")
    expect(isbn_converter("1-7982-0894-6")).to eq("978-1-7982-0894-6")
  end
end

Ok, I figured it out on the other one. It's because I was trying to add 1 to an index that didn't exist. So I guess in the above I am trying to do something similar. I will work it out...

Thanks for this, if I put a return in place of the puts, I get this error message: ./lib/solution.rb:8:in sum_of_differences': undefined method -' for nil:NilClass (NoMethodError)

Any ideas? It is working in vs code.

Actually I am getting the same error on a different kata. On this one it is because I am doing +1 on an array index, like I am in the code above. I think this is the problem. Do you know how to do this differently? Ta

Eventually I have passed! Thanks for your help :)

Right, got it. Thanks!

Thanks, I see what you mean about the while part. Sorry I don't understand what you mean about 10 and 11 being outputs not inputs. This is what I input into the function call.

Can you give me any clues about how to approach this?

Thanks, yeah once I understood what I actually had to do, I got there quite quickly. I've spent ages on that so I'm glad I finally passed. Must remember to read the question properly in future!!!

Help!!! I am so completely stuck on this but also, I cannot work out why this one has failed:

25,25,50,100,25,50,25,100,25,50,25,100,25,50,25,100,50,50

it says it expects NO but mine returns YES. Why isn't this yes?

My indices:
0: balance is 0, change required, 0, - YES + income 25
1: balance is 25, change required, 0 - YES + income 25
2: balance is 50, change required, 25 - YES + income 50
3: balance is 75, change required, 75 - YES + income 100
4: balance is 100, change required, 0 - YES + income 25
5: balance is 125, change required, 25 - YES + income 50
6: balance is 150, change required, 0 - YES + income 25
7: balance is 175, change required, 75 - YES + income 100
8: balance is 200 ($100 + $100), change required, 0 - YES + income 25
9: balance is 225, change required, 25 - YES + income 50
10: balance is 250, change required, 0 - YES + income 25
11: balance is 275, change required, 75 - YES + income 100
12: balance is 300, change required, 0 - YES + income 25
13: balance is 325, change required, 25 - YES + income 50
14: balance is 350, change required, 0 - YES + income 25
15: balance is 375, change required, 75 - YES + income 100
16: balance is 400, change required, 25 - YES + income 50
17: balance is 425, change required, 25 - YES + income 50

And from this point there is always enough change. Well, as I write this I realise I may have got the logic wrong. Am I right in thinking this is not just about total balance but the actual type of notes you have available in the till? In which case 16 would be a NO?

Gaahhhh looks like I need to start again right?