Lecture Notes on 21 Jan 2022

* Characteristics of good software design
- correct
- efficient: time & space
- maintainable
- elegant
- secure
- user friendly

* Writing test cases
def test_cases():
  # test the function longest_subsequence()
  assert longest_subsequence ("", "") == []
  assert longest_subsequence ("abcd", "abcd") == ["abcd"]
  assert longest_subsequence ("abcd", "bcef") == ["bc"]
  assert longest_subsequence ("abcd", "xyz") == []

  # other test cases

  return "all test cases passed"

* Write a function that gets all substrings of a string
# Input: s a string
# Output: returns a list of all substrings of s
def all_substr (s):
  # create a list to store all substrings
  substrs = []

  # get size of window
  wnd = len (s)

  # get all substrings
  while (wnd > 0):
    start_idx = 0
    while ((start_idx + wnd) <= len(s)):
      sub_string = s[start_idx: start_idx + wnd]
      substrs.append (sub_string)
      start_idx += 1
    # decrease the window size
    wnd = wnd - 1

  # return the result
  return substrs