CS 116: Introduction to Computer Science 2

CS 116 Tutorial 4: Lists, Mutation


Reminders: Assignment 4 is due on Wed, Jun 12th at 10am


    Questions 1, 2, and 3 use the following data definition:

    A Card is a list of length 2 where
    - the first item is an integer between 1 and 13, inclusive, representing the value of the card, and
    - the second item is a string ("hearts", "spades", "clubs", or "diamonds") representing the suit of the card.
    Example: [1, "hearts"] represents the ace of hearts


  1. Write a function create_cards that consumes a list of card values (integers between 1 and 13), and a list of suite values (one of the four suit strings), and returns a list of cards created pair-wise from the consumed lists (values and suits).
    Example: create_cards([4,1,10], ["hearts","diamonds","clubs"]) =>[[4,"hearts"], [1, "diamonds"], [10, "clubs”]].


  2. Write a function choose_by_colour that consumes a list of cards (hand) and a string "red" or "black" (colour) and returns a list of the values of the cards in hand of the appropriate colour (spades and clubs are "black", hearts and diamonds are "red").
    Example: choose_by_colour([[1,'hearts'], [9, 'spades'], [3,'diamonds']], 'red') => [1,3].

    Write this function twice. First, use explicit recursion. Then, use abstract list functions.


  3. a) Write a function flip_colour that takes in a card, c, and mutates the suit of that card to a different colour: if c is a heart, it is mutated to a spade (and vice versa), while if c is a club, it is mutated to a diamond (and vice versa).

    b) Write a function flip_hand that reads in a list of cards (hand), and mutates the suit of each card in the list so that their colours are flipped in the same way as in flip_colour.


  4. Write a function modify_list that consumes a list of integers (nums) and a single integer (n). The function returns None, but mutates the list in the following way:

    • If n does not appear in nums then add it to the end of nums.
    • If n appears once, then remove n from nums
    • If n appears at least twice, removes the first and last occurrences of n .

    For example:

    If L = [], modify_list(L,10) => None, and L = [10]
If L = [1,2,3], modify_list(L,10) => None, and L = [1,2,3,10]
If L = [1,2,3,4], modify_list(L,4) => None, and L = [1,2,3]
If L = [1,5,2,1,7,1,9], modify_list(L,1) => None, and L = [5,2,1,7,9]

  5. Write a function sanitize that consumes a string, s, and returns a similar string but with any non-alphanumeric characters removed.
    For example: sanitize("@Test@") => "Test"


  6. Write a function reversed_list a list of string, L, and returns a list containing the elements of L in reverse order. Write this function using abstract list functions.
    For example: reversed_list(["I","love","cs116"]) => ['cs116','love',I]