List Mutation (Module 4) Accumulative Recursion (Module 5) Efficiency (Module 7) Searching & Sorting (Module 8) Dictionaries (Module 9)

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Leonard Garrett
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1 Sherry & Pauline

2 List Mutation (Module 4) Review for CS 116!!! Accumulative Recursion (Module 5) Efficiency (Module 7) Searching & Sorting (Module 8) Dictionaries (Module 9) Class Objects (Module 9) Files (Module 10)

3 L33T speak is a different form of writing, usually online. It consists of replacing certain letters with symbols or numbers. Consider the table below of letters, and their corresponding L33T translations. Write a Python function called leet which consumes a list of strings, los, and mutates the list where each string becomes its leet version. The function returns None. Example: L = ["password", "secrets", "CS116 "] leet(l) L = ['p@$$w0r)', '$3(r3+$', '($116']

4 O(1): - +, -, *, /, =, max(a, b), min(a, b) - len(s), s[k], - len(l), L[k], L[3 : 5], L.append(x) - str.isupper(c) #c is a character O(n): - s.count(), s.find(), s.lower(), - L + [x], sum(l), max(l), min(l), L[1: ], list(range(n)), L.count(), L.index(), L.insert(), L.pop(), L.remove() - s + t is O(n + len(t)), L + M is O(n + len(m)) - L[a : b] is O(b - a), so at most O(n) O(n log n): - L.sort()

5 You can find this on page 28, Module 7! Also provided on the exam reference sheet.

12 def selection_sort(l): n = len(l) positions = list(range(n-1)) for i in positions: min_pos = i for j in range(i,n): if L[j] < L[min_pos]: min_pos = j temp = L[i] L[i] = L[min_pos] L[min_pos] = temp Before the loop:!(") Inner loop:!(") each iteration Outer loop:!(") iterations à!(") +!(")!(") =!(n^2)

13 def insert(l, pos): while pos > 0 and L[pos] < L[pos-1]: temp = L[pos] L[pos] = L[pos-1] L[pos-1] = temp pos = pos-1 def insert_sort(l): for i in range(1,len(l)): insert(l,i) insert_sort requires!(") calls insert requires at most!(") while loop iterations Each while loop body requires!(1) steps à!(")!(")!(1) à!("^2)

14 def mergesort(l): if len(l) < 2: return mid = len(l)//2 L1 = L[:mid] L2 = L[mid:] mergesort(l1) mergesort(l2) merge(l1,l2,l)!(") = #(") + 2!("/ 2) #(" log ")

15 key : value #a key value pair d[key] => value list(d.keys()) => listof keys in d list(d.values()) => listof values in d key in d => Bool d[new_key] = new_value # add new pairs to d d[key] = new_value # reassign a new value to key

16 d1 = {1: "review for CS 116", 2: "Sure", 3: "Why not?", 4: "Good luck on final"} d1[1] = "review for CS 116" d1.keys() = ["review for CS 116", "Sure", "Why not?", "Good luck on final"] ** Note: the order is not guaranteed ** 5 in d1 => False d1[5] = "holiday" d1 = {1: "review for CS 116", 2: "Sure", 3: "Why not?", 4: "Good luck on final", 5: "holiday"}

17 Complete the Python function common that consumes two dictionaries (d1 and d2, with common key and value types). Return a list of all the keys (in increasing order) that occur in both d1 and d2 and have the same associated values in each. Examples: common({1:'1', 2:'2', 4:'4'}, {3:'3', 2:'2', 1:'1', 4: 4 }) => [1,2] common({1:'1', 2:'2', 4:'4'}, {3:'3', 5:'2', 6:'1 }) => []

18 There are 3 magic methods that you have to define inside of Class in CS 116: init : Constructor that initializes the fields of a class when an object is created repr : Returns a printable representational string of the given object eq : Allows you to compare if two objects are equal (have equal fields values)

19 Use the form: self.field Examples: - Country.continent - Country.leader - Country.population

20 class Movie: ''' fields: title (Str), year (Nat), stars (listof Str) requires: year is the year the movie was released (> 1900) stars includes the names of the actors in the movie ' def init (self, name, date, actors): self.title = name self.year = date self.stars = actors def repr (self): return "{0}({1}) featuring {2}".format( self.title, self.year, self.stars) def eq (self, other): return isinstance(other, Movie) and \ self.title == other.title and \ self.year == other.year and \ self.stars == other.stars

21 Complete the class function add_star that consumes a Movie object and a string, star, and add the star's name to the end of the movie s stars list. In addition, the function returns the number of actors listed under stars. Examples: princess_bride = Movie("Princess Bride", 1987,["Cary Elwes", "Robin Wright", "Mandy Patinkin"]) princess_bride.add_star("andre the Giant") => 4 princess_bride = Movie("Princess Bride", 1987,["Cary Elwes", "Robin Wright", "Mandy Patinkin", "Andre the Giant"])

22 Write a function movies_by_year that consumes a list of Movie objects and returns a dictionary where the keys are the years the movies came out in and the associated values is a list of the movie titles ( if two movies came out in the same year then both their titles would be in the associated list for that key) Example: m_list = [Movie("Princess Bride", 1987,["Cary Elwes", "Robin Wright","Mandy Patinkin"]), Movie("Alien Nation", 1988, ["James Caan", "Mandy Patinkin"]), Movie("RoboCop", 1987, ["Nancy Allen", "Peter Weller"])] movies_by_year(m_list) => {1987: ['Princess Bride', 'RoboCop'], 1988: ['Alien Nation']}

23 f = open(filename, r ) è open the file for reading f = open(filename, w ) è open the file for writing f.readline() è return the next line f.readlines() è return the list of all the lines f.write(s) è append s to end of f f.writelines(los) è append los to end of f f.close() è close f to prevent losing data

24 Write a Python function num_words that consumes the name of a filename and returns the the number of words in the file Note: words are considered characters separated by a space and there are only letters in the file Examples: If "test1.txt" contains "I love Computer Science\n, then num_words("test1.txt") => 4 If "test2.txt" is an empty file, then num_words("test2.txt") => 0

25 Write a function write_reverse that reads in the contents from the input file, infile, and writes all of the lines in reverse to an outfile where outfile is a filename entered by the user and returns None Examples: If "test1.txt" contains "I love Computer Science\n, then write_reverse("test1.txt") would write the line "ecneics retupmoc evol I\n" to the file "output1.txt" where "output1" is the filename entered by the user. If "test2.txt" is an empty file then write_reverse("test2.txt") would write nothing to "output2.txt" where "output2" is the filename entered by the user

26 Terminologies: Vertex & Edge Neighbours & Degree Connected graph vs. Unconnected graph Make sure you are familiar with different representations of a graph: Vertex and Edge list representation Adjacency list representation Adjacency matrix representation (call 'A' vertex 0, 'B' vertex 1, etc.) ~Please review Tutorial 11~

Module 08: Searching and Sorting Algorithms

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