Gotcha, great!

You can click 'view solution' under my message to see the O(n) answer. If you're asking about the complexity calculations themselves, try the book 'Elements of Programming Interviews'.

Where does one learn about that now?

The line "if l!=2:" is redundant, though I also suggest using elif and else for clarity

This solution increments checked numbers by 1, but we can increment the right-most unit once maxSum is exceeded. For example, if maxSum is 3 and the current number is 190000, enourmous time is saved by incrememting by 10000 rather than 1.

See my implementation here. achieving 1650ms compared to this solution's 3200ms. There are also ways to further improve the incrementing efficiency.

https://www.codewars.com/kata/reviews/55f6846f1eb6c5b0f000006a/groups/62ffe16b747aae000149c41c