Problem Solving

Lists

Rotate:

def rotate(l, k):
  for i in range(k):
    l.insert(0, l.pop())
  return l
  
  # option 2:
  def rotate_alternative(lst, degree):
  rotation = degree % len(lst)
  return lst[-rotation:] + lst[:-rotation]

Optimized version:

  # Idea behind this: 
  # <> marks selected elements

# 2 rotations
['a', 'b', 'c', 'd', 'e', 'f'] 

# reverse first 2
[<'b', 'a',> 'c', 'd' ,'e', 'f'] 

# reverse all but first 2
['b', 'a', <'f', 'e', 'd', 'c'>] 

# reverse all
[<'c', 'd', 'e', 'f', 'a', 'b'>] 

# all done!
['c', 'd', 'e', 'f', 'a', 'b'

def rev(lst, low, high):
  while low < high:
    lst[low], lst[high] = lst[high], lst[low]
    high -= 1
    low += 1
  return lst


def rotate(my_list, num_rotations):
  # Reverse first num_rotations
  rev(my_list, 0, num_rotations-1)
  # Reverse all but num_rotations
  rev(my_list, num_rotations, len(my_list)-1)
  # Reverse all
  rev(my_list, 0, len(my_list)-1)
  
  return my_list