The input array will always be valid!

thank you for explanation

If it helps, list comprehension is of the form:

L = [A for x in X for y in Y for z in Z if B]

Which can be written as:

L = []
for x in X:
  for y in Y:
    for z in Z:
      if B:
        L.append(A)

You can put as many for as you want, and of course you can put list comprehension inside list comprehension:

L = [[A for x in X] for y in Y]

Which can be written as:

L = []
for y in Y:
  temp = []
  for x in X:
    temp.append(A)
  L.append(temp)

It took me some time to understand which for was done first when I started.

It's a list comprehension, with an if statement (and an index). A very useful structure, even if it's not easy to grasp at first. Read more here: https://docs.python.org/3/tutorial/datastructures.html#list-comprehensions

me too :)

All tests pass, time limit execution fails for the reason "Time: 12303ms Passed: 0 Failed: 0".
The 'Atom' editor shows "Running: python (cwd=undefined pid=733). Exited with code=0 in 0.217 seconds."

Does anybody have the best timing for this kata?

I did not find a way to cut down time at all !!!

Thanks!