Find maximum possible time HH:MM by permuting four given digits

Question

I recently took a coding test for a promotion at work. This was one of the tasks I really struggled with and was wondering what is the best way to do this. I used a load of

Answer 1

For places, AB:CD,

If at any point a condition cannot be fulfilled:
  return NOT POSSIBLE

If there are two numbers greater than 5:
  place the larger in B, smaller in D

for non-filled places from left to right:
  if B > 3:
    place a 1 in A
  else:
    place the largest number smaller than 3 in A

  if A is 2:
    place the largest number smaller than 4 in B
  else:
    place the largest number in B

  place the largest number smaller than 6 in C
  place the remaining number in D