Quiz 3 Information

Quiz details

• Quiz 2 will be held on Monday 6/1 , beginning promptly at 9:30am.

• The quiz will be on paper, and you will be expected to write/explain some code that is similar to work you did in the problem set.

• Expect 2 short questions.

  You will have 20 minutes for the quiz including.

• This quiz is closed notes/closed books, and without any use of reference materials. No computers, phones, AI glasses, or other electronic devices are permitted.

• There are some sample/pratice questions at the bottom of this page.

Material covered

The quiz will focus on the material that we have covered in module 3 and problem set 3. You must be familiar with concepts and syntax that were introduced in the pre-class videos, in-class discussion, or on the problem sets even if they were not covered in the videos or readings, specifically including:

• Recursive functions with numeric data/results

• Recursive function that process a sequence (e.g., string or lists)

• Recursive functions that generate a sequence (e.g., string or list)

• Recursive functions that process 2 sequences (e.g., string or list) at a time

You also are expected to remember everything that was including in quiz 2, e.g., writing functions, arithmetic, decision statements, etc.

Preparing for the quiz

• One way to prepare is to review the videos and readings and class notes and make a summary of the key points in your own words. “Summarizing” the material in this way is a great way to ensure that you really understand the key concepts.

• We also encourage you to do practice problems. Options include:

  • redoing the problems from the problem sets

  • additional practice problems (below)

• When working on practice problems, try to come up with your answers on paper, rather than through a trial-and-error approach in Spyder or in another programming environment. This will be give you an experience that is similar to the one that you have during the quiz.

• Feel free to post questions about the quiz on Piazza (using the quiz3 tag).

Additional practice problems

1. What is printed by the following working Python program?

   def mystery(x):
       print('x is', x)
       if x < 1:
           return 2
       else:
           p = 6 - mystery(x - 1)
           print('p is', p)
           return p
   
   y = mystery(3)
   print('y is', y)
   

2. Write a function count_ones(s) that takes in a string s of '0's and '1's and returns the number of '1's in the input. Use recursion.

3. Write a recursive function sum_list(values) that returns the sum of all numbers in a list. You may not use any built-in functions. >>> sum_list([1, 2, 3, 4]) 10 >>> sum_list([5, -3, 2]) 4 >>> sum_list([]) 0

4. Write a function swap_bits(s) that takes in a string s of '0's and '1's and returns a string in which each bit in s has been swapped/replaced with the other bit. For example, swap_bits('101011') should return '010100'. Use recursion.

5. Write a function count_transitions(s) that takes in a string s of '0's and '1's and returns the number of times there is a transition from a '0' to a '1' or vice-versa in that input string. For example, count_transitions('1110110000') should return 3. Use recursion.

6. Write a function abs_values(values) that takes a list of integers values and returns a new list containing the absolute values of each element in values. For example, abs_values([3, -4, 5, -6, 7]) will return [3, 4, 5, 6, 7]. Use recursion.

7. Write a function join(strings, separator) which takes a list of strings and a separator (a string), and produces a result that is a string containing all of the elements in the list, separated by the separator. For example: join(['the','long','and','winding','road'], ' ') would return 'the long and winding road' (note the lack of trailing space). Use recursion.