Joseph Surin
Computing & Software Systems @ The University of Melbourne

CTF Writeups/Projects/Random Stuff
Unimelb programming proficiency test

# Overview

The Semester 1, 2019 Unimelb programming proficiency test was held today. The test is a simple 90 minute test that allows students who acheived 75%+ to skip COMP10001 and enrol in COMP10002 straight away.

This year's test had 6 questions, 4 of them being simple function implementations, 1 being a short response question, and 1 being a slightly more challenging function implementation.

The questions were geared towards Python, although you were allowed to use any language you wanted as long as you indicated that on the answer sheet. I'm not completely sure how marks will be awarded, but the test stated on the front that inefficient algorithms won't be penalised.

### The questions

The questions below are how I recall them from the test. The wording may not be exactly the same and my sample solutions might have some mistakes in them.

## Question 1: Palindromes [15 marks]

Write a function is_palindrome that takes a string word and returns True if the word is a palindrome and False otherwise. A palindrome is a word that reads the same backward as forward, for example madam is a palindrome, but programming is not.

### Sample solution

def is_palindrome(word):
return word == word[::-1]

## Question 2: Framed Message [15 marks]

Write a function frame that takes a list of strings wlist and prints the message in a frame of asterisks * such that the longest word in the list is just touching the edges of the frames. For example:

> frame(['COMP10001', 'is', 'fun'])

***********
*COMP10001*
*is       *
*fun      *
***********

### Sample solution

def frame(wlist):
width = 2 + max(map(lambda w: len(w), wlist))
print('*' * width)
for w in wlist:
print('*' + w.ljust(width - 2, ' ') + '*')
print('*' * width)

## Question 3: Median Letter [15 marks]

Write a function medianL that takes a string word consisting of only lower case alphabet letters and returns a string with the median letter capitalised. The median letter in this case refers to the letter that sits above half of the letters and below the other half of the letters in the word. For example in the word predict, d is the median letter, and so medianL('predict') returns preDict. If the word has an even number of letters, the median letter is defined to be the rightmost letter of the two letters that exhibit the 'median' property. For example in the word orange, n is the median letter, and so medianL('orange') returns oraNge.

### Sample solution

def medianL(word):
m = len(word) // 2
return word[:m] + word[m].upper() + word[m+1:]

## Question 4: Missing Letters [20 marks]

Write a function missing_letters that takes two strings word1 and word2 and returns a string containing the letters that need to be added to word2 to make up word1 (in the order they appear). Each character should only be considered once. For example, missing_letters('classes', 'lass') should return ces, and missing_letters('woololomng', ol) should return woolomng. An empty string should be returned if word1 is the empty string as no additional characters can be added to word2 to make up word1.

def missing_letters(word1, word2):
letters = ''
for l in word1:
if l not in word2:
letters += l
else:
word2 = list(word2)
word2.remove(l)
word2 = ''.join(word2)
return letters

## Question 5: Grid Words (challenging) [15 marks]

Write a function valid_word that takes two parameters: board and word, and returns True or False depending on whether or not word can be formed by connecting adjacent letters in the board. The board is represented as a 2 dimensional list of any size (n x m). An adjacent letter is a letter that is directly above, to the right, below or to the left of a letter.

For example, if the board is as given below, calling valid_word with the words ABC or AESAG would return True, while calling it with the words CDE or ESACF would return False

A B C D
E S A C
F E G A

### Sample solution

def valid_word(board, word):
w = len(board[0])
h = len(board)

return list(filter(lambda p: p[0] >= 0 and p[0] <= h-1 and p[1] >= 0 and p[1] <= w-1,
[(r-1,c), (r, c+1), (r+1, c), (r, c-1)]))

def valid_word_r(p, word):
l = word[0]
al = map(lambda a: board[a[0]][a[1]], adj)

if l not in al: return False
if len(word) == 1: return True

np = [a for a in adj if board[a[0]][a[1]] == l]
return any(map(lambda p: valid_word_r(p, word[1:]), np))

sp = [(i, r.index(word[0])) for i,r in enumerate(board) if word[0] in r]
if len(word) == 1 and word[0] in map(lambda a: board[a[0]][a[1]], sp): return True
elif len(word) == 1: return False

return any(map(lambda a: valid_word_r(a, word[1:]), sp))

(I obviously did not know about list comprehensions at this point in time)

## Question 6: Short Answer Responses [10 marks]

### Part A [4 marks]

How many multiplication operations occur in the following code for any given M and N?

res = 0
for i in range(1, M+1):
for j in range(1, M-N+1):
res += i * j

### Sample solution

$((M+1)-1) \times ((M-N+1)-1)$ $= M^2 - MN$

### Part B [6 marks]

How many times does Function get called when called with the parameter twydlyllyngy?

def Function(word):
if len(word) == 0:
return 0
elif len(word) == 1:
if word in 'aeiou':
return 1
else:
return 0
else:
mid = int(len(word) / 2)
return Function(word[:mid]) + Function(word[mid:])

### Sample solution

twydlyllyngy -> twydly, llyngy

twdly -> twy, dly
llyngy -> lly, ngy

twy -> t, wy
dly -> d, ly
lly -> l, ly
ngy -> n, gy

wy -> w, y
ly -> l, y
ly -> l, y
gy -> g, y

Total 23 calls including the initial call.