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

HATE RETURN

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

range(1,7)

the last number (stop=7) is not included in the range function so when you write 7 the iteration of the for loop will stop in the number 6 (since the 7 is not included)
so when you want to stop in 7 you should do 7+1

Oooooh, I just got it! Brilliant!

the same way i solved problem. which is faster? replace or repeat?

Oh, I totally forgot that range can do this.

dropped it into C++ ;)

damn forget about that one

i had the same idea, just used a string instead :(