Questions

This review is not comprehensive of all content that will be on the final exam, but rather provides a few extra practice questions and some questions on concepts after quiz 3. Previous quizzes/practice questions are also valuable in reviewing for the final exam. Lecture videos are another valuable resource.

Solutions for each problem can be found at the bottom of this page. Keep in mind that there may be multiple solutions to each problem.

Function Writing

1. Write a function called reverse_multiply. Given a list[int], reverse_multiply should return a list[int] with the values from the original list doubled and in reverse order.
   Example: reverse_multiply([1, 2, 3]) should return [6, 4, 2].

2. Write a function called free_biscuits. Given a dictionary with str keys (representing basketball games) and list[int] values (representing points scored by players), free_biscuits should return a new dictionary of type dict[str, bool] that maps each game to a boolean value for free biscuits. (True if the points add up to 100+, False if otherwise)
   Example: free_biscuits({ “UNCvsDuke”: [38, 20, 42] , “UNCvsState”: [9, 51, 16, 23] }) should return { “UNCvsDuke”: True, “UNCvsState”: False }.

3. Write a function called multiples. Given a list[int], multiples should return a list[bool] that tells whether each int value is a multiple of the previous value. For the first number in the list, you should wrap around the list and compare this int to the last number in the list.
   Example: multiples([2, 3, 4, 8, 16, 2, 4, 2]) should return [True, False, False, True, True, False, True, False].

4. Write a function called merge_lists. Given a list[str] and a list[int], merge_lists should return a dict[str, int] that maps each item in the first list to its corresponding item in the second (based on index). If the lists are not the same size, the function should return an empty dictionary.
   Example: merge_lists([“blue”, “yellow”, “red”], [5, 2, 4]) should return {"blue": 5, "yellow": 2, "red": 4}.

5. Write a function named reverse_string that reverses the characters of a string without using the reverse built-in function.

Class Writing

5. Create a class called HotCocoa with the following specifications:
   1. Each HotCocoa object has a bool attribute called has_whip, a str attribute called flavor, and two int attributes called marshmallow_count and sweetness.
   2. The class should have a constructor that takes in and sets up each of its attribute’s values.
   3. Write a method called mallow_adder that takes in an int called mallows, increases the marshmallow_count by that amount, and increases the sweetness by that amount times 2.
   4. Write a method called calorie_count that returns a float. If the flavor of the HotCocoa is “vanilla” or “peppermint”, increase the calorie count by 30, otherwise increase it by 20. If the HotCocoa has whipped cream (has_whip is True), increase the calorie count by 100. Finally, increase the calorie count by half the number of marshmallows. The calorie count should be calculated and returned when this method is called.
6. Create a class called TimeSpent with the following specifications:
   1. Each TimeSpent object has a str attribute called name, a str attribute called purpose, and an int attribute called minutes.
   2. The class should have a constructor that takes in and sets up each of its attribute’s values.
   3. Write a method called add_time that takes in an int and increases the minutes attribute by this amount. The method should return None.
   4. Write a method called reset that resets the amount of time that is stored in the minutes attribute. The method should return the amount that was stored in minutes.
   5. Write a method called report that prints a line reporting information about the current TimeSpent object. Suppose a TimeSpent object has name = “Ariana”, purpose = “screen time”, and minutes = 130. The report method should print: “Ariana has spent 2 hours and 10 minutes on screen time.”

Recursion

7. What is it that makes a function/structure recursive?
8. A recursive function must have a recursive case. (T/F)
9. A recursive function may define multiple recursive cases. (T/F)
10. What happens if a recursive function does not make progress toward a base case?
11. Write a recursive factorial function. The factorial of a positive integer is the product of that integer with all of the positive integers less than it. !n is used to denote the factorial of a positive integer n. (4! = 4*3*2*1 = 24) Ex: factorial(4) should return 24, factorial(5) should return 120, factorial(1) should return 1.
12. Diagram the following call to factorial using the solution provided below.
13. EXTRA PRACTICE: Diagram calls to functions from EX10: Linked List Utils. For obvious reasons, we cannot provide solutions to these, but having practice diagramming recursive structures as well as recursive functions such as factorial is great practice for the final! The examples in lecture videos can be helpful if this is difficult, and as always office hours is a great resource if you struggle with this.

Solutions

Function Writing

def reverse_string(input: str) -> str:
    """Reverse the characters of a string without using reverse."""
    result: str = ""
    i: int = len(input) - 1
    while i >= 0:
        result += input[i]
        i -= 1
    return result

Class Writing

Recursion

7. A recursive function is a function that calls itself, and recursive structures are defined in terms of themselves.
8. T
9. T
10. If a recursive function does not make progress toward a base case, it will result in infinite recursion and python will stop its execution with a RecursionError.
11. 
12.