COSC 101: Exam 3 Practice Problems

Problem #1

Assume that the following statement have already been executed in the interactive interpreter:

a = "radio cure"
b = [ 1, 1, 2, 3, 5 ]
c = 3

For each of the following expressions, evaluate the expression and write the resulting value, or identify the error in the code that would prevent it from running.

len(b) // c
b[5] > len(a)
a[2:-2:2]
c in b
len(b[:3])
b[::2].append(-13).sort()
b.pop(2) == c
a[-2] + a[5] + a[0]

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Problem #2

Given a string s with an odd length:

Write an expression to print the middle character. For example, if s is 'exam3' the expression should print 'a'.
Write an expression to print the string up to but not including the middle character. For example, if s is 'exam3' the expression should print 'ex'.
Write an expression to print from the middle character to the end, not including the middle character (i.e., from one after the middle to the end). For example, if s is 'exam3' the expression should print 'm3'.

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Problem #3

Given the string s='abcdefghij', write a string slice expression that will print the following:

'jihgfedcba'
'adgj'
'igeca'

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Problem #4

Write a function named countsubstr that takes two strings as parameters and returns the number of times that the second string appears in the first string. For example:

>>> countsubstr('aabbabab','ab')
3
>>> countsubstr('computersarecomputational','comp')
2

You cannot use any built-in string methods for this problem (but you can use slicing).

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Problem #5

Write a function makeAcronym that takes a phrase (a string) as a parameter, and creates and returns a new string that contains the first letter of each word in the phrase, capitalized. For example, makeAcronym('Gnus not UNIX') should return the string 'GNU'. For this problem, you can use any string methods you’d like. For example: upper(), lower(), count(), find(), or split().

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Problem #6

Write a function removeAs that takes a string as input and returns the string with all as removed. For example, if you call removeAs('amalgamate'), the function should return the string 'mlgmte'. Your function should remove both lower-case and upper-case A’s but should not change any other characters.

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Problem #7

Write a function arrange_names that takes a name in the form of "Doyle, Arthur Conan", and returns the name in the form "Arthur Conan Doyle," (alphabetical order).

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Problem #8

Write a function guess_letters that takes a word (a string) as a parameter and repeatedly asks the user to guess the letters in the word. The user should be asked for a new letter while he/she has not guessed all the letters in the word. Prior to each guess the user makes the function should print the letters that have been successfully guessed, as well as the number of letters remaining to be guessed. The function should return the number of guesses taken to get all the letters.

The guessing should all be done in a case-insensitive way (you can just convert to upper case everywhere). You are encouraged (but not required) to write a helper function.

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Problem #9

Write a function is_anagram that takes two strings as parameters and to decide whether one is a permutation of the other. For example, if you are given "cinema" and "iceman", you should return True, since these strings are anagrams.

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Problem #10

Write a function is_rotation that takes two strings as parameters and tests whether one string is a rotation of another, e.g., "waterbottle" and "erbottlewat". The function should return True if one string is a rotation of another and False otherwise.

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Note: problems 11-16 were removed from this practice set because they address concepts and syntax not covered on this exam.

Problem #17

Write a function countevens that takes a list of integers as a parameter and returns a count of the number of even values in the list. For example:

>>> countevens([2,1,2,3,4])
3
>>> countevens([2,2,1])
2

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Problem #18

Write a function named sum67 that takes a list of integers as a parameter, and returns the sum of the numbers, except that it should ignore sections of numbers that start with a 6, extending to the next 7. (You can assume that every 6 will be followed by at least one 7). For example:

>>> sum67([1,2,2])
5
>>> sum67([1,2,2,6,99,99,7,1])
6
>>> sum67([6,6,1,2,3,4,5,6,7,7])
7

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Problem #19

Write a function sumSquares that takes a list of numbers and computes and returns the sum of each number squared. For example, if the function is given the list [2,3,4] as a parameter, it should return 29 (4 + 9 + 16).

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Problem #20

Write a function removeOdd1 that takes a list of integers as a parameter, and returns a new list that contains only the even (non-odd) numbers from the list passed as a parameter. You should not modify the list passed in as a parameter.

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Problem #21

Write a function removeOdd2 that takes a list of integers as a parameter and removes all the odd values in the list in place. The function should not return anything.

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Problem #22

Write a function mostFrequent that finds the most commonly occurring items in a list, and returns a list of those items. For example given a list [1,2,3,4,4,4,2,1,2,0,5], the function should return [4,2] since those items occur 3 times, which the maximum number of times any item occurs in the list. You can use any list methods.

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Problem #23

Write a function sumOddsLt7 that takes a list of positive integers and returns the sum of the odd values that are less than 7. For example, if the list [1,2,3,4,9,1,2,3,4] is passed as the parameter, the function should return 8 (1+3+1+3).

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Problem #24

Write a function removeOddsLe7 that takes a list of positive integers and returns a new list of integers in which only even numbers less than or equal to 7 remain. The list passed as a parameter shouldn’t be modified inside the function. For example, if the list [1,2,3,4,9,1,2,3,4,9] is passed as the parameter, the function should the list [2,4,2,4].

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Problem #25

Write a function secondLargest that takes a list of integers as a parameter, and finds the second largest unique element in the list. To help, there are two useful functions built in to Python, max and min, that return the largest and smallest elements of a list, respectively.

You should not modify any element in the list. (You can make a copy of the list and modify the copy.)

>>> secondLargest([1,2,3,3,4,4,5,5])
4

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Problem #26

Write a function named fractionsmaller that takes a list of numbers and a single number as parameters. The function should return the fraction of values in the list that are smaller than the value given as the second parameter. You should not modify the list given as the first parameter.

For example:

>>> fractionsmaller( [1,4,3,2,5], 3 )
0.4
>>> fractionsmaller( [5,2,3,6,10,2,55,3], 12 )
0.875
>>> fractionsmaller( [5,7,10], 4 )
0.0
>>> fractionsmaller( [1,2,3], 10 )
1.0

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Problem #27

What is the output of the following code:

def mystery1(xlist):
    while len(xlist) > 3:
        xlist.remove(max(xlist))

mylist = [ 42, 5, 10, 6, 7, 10, 4 ]
mystery1(mylist)
print (mylist)

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Problem #28

What is the output of the following code:

def mystery3(i, list1, list2):
    i = i + 4
    list1[-1] = 42
    list2 = list1

i = 2
one = [4, 10]
two = [-1, -1]
mystery3(i, one, two)
print(i)
print(one)
print(two)

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Problem #29

Write a function find_reverse_pairs that reads a text file containing a series of words, one per line, and finds all the pairs of words in which one word is equivalent to the other word spelled backwards. The word pairs should be returned as a list of sublists (each sublist should contain a given word pair; all sublists of word pairs should be added to the list that is returned from the function).

For example, if the file contains:

tic
tac
toe
computer
science
tab
bat
dog
cat

the resulting list will be [['cat', 'tac'], ['bat', 'tab']].

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Problem #30

Write a function is_subset that takes two lists as a parameter and returns True if all the elements in the second list are also present in the first list (i.e., the second list forms a subset of the elements in the first list). Return False otherwise. Only use while loops in your solution. For example:

>>> is_subset([1,2,3,4,5], [1,2,3])
True
>>> is_subset([1,2,3,4,5], [1,2,3,4,5,6])
False
>>> is_subset([1,2,3,4,5], [])
True

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Problem #31

Write a function average_of_freeze_streak that takes a list of integers representing daily low temperatures, in Fahrenheit degrees. Find the longest consecutive series of freezing temps (<= 32 degrees) in number of days, and return the average temperature of that series of temps. For example:

>>> print(average_of_freeze_streak([]))
None
>>> print(average_of_freeze_streak([33,40,50,60]))
None
>>> print(average_of_freeze_streak([30,40,45,37,33,30,29,28,40,45]))
29.0

Only use while loops in your solution. You can assume that the list passed as a parameter is non-empty. If there are no freezing (or below) temperatures in the list, you should just return None. If there are streaks of the same length in the list, you can return the average of any of them.

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Problem #32

Write a function count_chars that takes a list of strings and a one character string. Find and return the count of that character among all the strings in the list. For example, given the list ["apple","banana","pear"], and the character "p", the function should return 3 (two p’s in apple and one in pear).

You can only while loops in your solution. You must write a helper function.

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Problem #33

Write a function unique_chars that takes a string and returns True if all characters in the string are unique, and False otherwise. You should use while loops in your solution (no for loops).

>>> unique_chars('abcdefghijklmnopqrstuvwxyz')
True
>>> unique_chars('hello')
False
>>> unique_chars('help!')
True

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Problem #34

Write a function numBefore that takes two parameters: a non-empty string and a single character string. The function returns the number of letters in the string that are strictly before the given character in the alphabet, ignoring case. For example:

>>> numBefore('hello', 'h')
1
>>> numBefore('hello', 'z')
5
>>> numBefore('hello', 'a')
0

Your solution should only contain while loops; no for loops are allowed.

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Problem #35

Consider a nested list that contains “shopping cart” items for an online store. The nested list is structured as follows: each sublist contains (1) a product category, like “clothes”, or “electronics”, (2) a product name like “Merino wool socks, Unisex L, black”, “1080p HD Adventure Camera”, and (3) a product price as a floating point number.

Write a function called cartCategorySum that accepts two parameters: a nested list (as described above) and a category name. The function should compute the sum of prices for all products within the given category. Note that the category given as the second parameter to the function may be in a different case than the category indicated in the list of cart items.

For example, cartCategorySum([['toys', 'slinky', 1.5], ['toys', 'ball', 3.5], ['electronics', 'laser pointer', 11.99]], 'TOYs') should return 5.0.

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Problem 36

Consider again a nested list that contains “shopping cart” items for an online store. The nested list is structured as follows: each sublist contains (1) a product category, like “clothes”, or “electronics”, (2) a product name like “Merino wool socks, Unisex L, black”, “1080p HD Adventure Camera”, and (3) a product price as a floating point number.

Write a function called cartCategoryProducts that accepts two parameters: a nested list (as described above) and list of category names. The function should return a list of products where the product category is contained in the category list. The product name in the list returned should be given in “title case” (use the title method on strings). The order of the items within the list returned doesn’t matter.

For example, cartCategoryProducts([['toys', 'slinky', 1.5], ['toys', 'ball', 3.5], ['electronics', 'laser pointer', 11.99]], ['TOYs']) should return ['slinky', 'ball'].

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Problem 37

Write a function called sortCartProducts that accepts one parameter: a nested list (as described above). The function should create a new list containing sublists of only the product name and price, with product names in “title case” (use the .title() string method). The list contents should be sorted by product price in descending numeric order (i.e., most expensive items first). The sortCartProducts should not modify the list given as a parameter.

For example, sortCartProducts([['toys', 'slinky', 1.5], ['toys', 'ball', 3.5], ['electronics', 'laser pointer', 11.99]]) should return [['laser pointer', 11.99], ['ball', 3.5], ['slinky', 1.5]].

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