what ' , x ' means in lambda?

youre close to your given runtime but using arr1.sort() and arr2.sort() at the start ruins it - try arr1.reverse() and arr2.reverse() instead

This entirely defeats the point of the problem, that being to take advantage of the fact that the arrays are already sorted.

same

nice radix conversion from int to string

counting matches of '1' is simple, and could easily scale to higher radixes such as octal
could easily be extended to match multiple digits, such as .count('137')

range traversal is clear

accumulator function sum() over a list is also a nice aggregate function

Well, having to figure it out in native code on your own makes it a great kata on dynamic programming.

How does this have anything to do with math?

that is a smart solve ,, i like it , i know that is don't best practice and there was more solutions is more readable than it's but this is a new practice and a new way for the solution for me, so i like it.
i know my english language is bad :)

First time I notice that if R and or G if greater than B we get yellow :D :D :D
But overall nice one ;)

C# Translation

Approved

python new test frameworks

it doesn't work for None