Univalue list

univalue_list.py

# recursive approach
# time = O(n)
# space = O(n)
def is_univalue_list(head, prev=None):
  if not head:
    return True

  if head.val == prev or not prev:
    return is_univalue_list(head.next, head.val)
  else:
    return False

# iterative approach
# time = O(n)
# space = O(1)
def is_univalue_list(head):
  first = head.val
  head = head.next

  while head:
    if head.val != first:
      return False
    head = head.next

  return True