### How did they do all that in one line? A Codewars challenge explanation

#### Erik Kristofer Anderson on August 06, 2019

Today I worked on a challenge on Codewars and saw a very concise solution submitted by another user on the site. I'll first just show the code, the... [Read Full]

Nested list comprehensions, nice :)

I wonder if the casts between int and str are necessary though.. perhaps there is a solution involving a more traditional add and carry approach?

Yeah, I thought it was a neat solution. :)

I'm not familiar with add and carry approaches, but it's interesting to consider whether it's possible without the casts.

I got bored and had a go. Please do not look at my code.....:)

``````def up_array(arr):
res = reduce(lambda r, x: (r[0]+[(x+r[1])%10],(x+r[1])/10), arr[::-1], ([],1))
return (res[0]+[1])[::-1] if res[1]>0 else res[0][::-1]

print up_array([2, 3, 9])
print up_array([9, 9, 9])
print up_array([9, 9, 0])
print up_array([2, 9, 9])
print up_array([9,9,9,9,9,9,9,9])
``````
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