Description
For this assignment, I provided you with starter code in file called a5_xxxxxx.py. Begin by replacing xxxxxx in the file
name with your student number. Then open the file. Your solution (code) for the assignment must go into that file in the
clearly indicated spaces. The file has main completely coded for you. Nothing else will go into the main. It also has some
functions completely precoded for you. Your task will be to code the remaining functions. You are not allowed to delete or
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comment-out any parts of the provided code. The only exception to that rule is the keyword pass. Some functions have that
keyword. You can remove it once you are done coding that function. You also must follow the instructions given in comments
and implied by docstrings. You are however allowed to add your own additional (helper) functions. In fact, you should add at
least one more function.
I have provided 5 text files to test and debug your code with as explained in the next section.
To submit the assignment, create a folder called a5_xxxxxxx where (as usual) you must replace xxxxxx in the file name
with your student number. Place your solution file a5_xxxxxx.py into that folder. Zip the folder and submit it. Do not use
winrar to create .rar file instead of .zip file. (No need to submit a5_xxxxxx.txt as proof that you tested your function. By
now we trust that you learnt and understand the need and importance for testing your functions and code in general).
As always, your program must run without syntax errors. In particular, when grading your assignment, TAs will first open
your file a5_xxxxxx.py with IDLE and press Run Module. If pressing Run Module causes any syntax error, the grade for the
assignment becomes zero. Furthermore, for each function whose code is missing, I have provided below one or more tests to test
your functions with. To obtain a partial mark for these functions your solutions may not necessarily give the correct answer on
these tests. But if your function gives any kind of Python error when run on the tests provided, that function will be marked
with zero points. Finally, each function has to be documented with docstrings.
There is also a5-more-example-runs.txt file, giving additional example runs to those given in the next section. The
behaviour of all example runs below and in a5-more-example-runs.txt should be considered as an implied requirement for
the assignment – as always.
Using global variables inside of functions is not allowed. If you do not know what that means, for now, interpret this to
mean that inside of your functions you can only use variables that are created in that function. For example, the following
code fragment would not be allowed, since variable x is not a parameter of function a_times(a) nor is it a variable created in
function a_times(a). It is a global variable created outside of all functions.
def a_times(a):
result=x*a
return result
x=float(input(“Give me a number: “))
print(a_times(10))
1 Social Networks: friends recommendations and more – 100 points
Have you ever wondered how social networks, such as Facebook, recommend friends to you? Most of the social networks use
highly sophisticated algorithms for this, but for this assignment you will implement a fairly naive algorithm to recommend the
most likely new friend to users of a social network. In particular, you will recommend the most probable user to befriend based
upon the intersection of your common friends. In other words, the user that you will suggest to Person A is the person who
has the most friends in common with Person A, but who currently is not friends with Person A.
Five text files have been provided for you to run your program with. Each represents a social network. Three are small
test files containing a made-up set of users and their friendships (these files are net1.txt, net2.txt and net3.txt). The two are a
subset of a real Facebook dataset, which was obtained from: https://snap.stanford.edu/data/egonets-Facebook.html
The format of all five files is the same:
The first line of the file is an integer representing the number of users in the given network.
The following lines are of the form: user_u user_v where user_u and user_v are the (non-negative integer) IDs of two users
who are friends.
In addition user_u is always less than user_v
For example, here is a very small file that has 5 users in the social network: 5
0 1
1 2
1 8
2 3
The above is a representation of a social network that contains 5 users.
User ID=0 is friends with User IDs = 1
User ID=1 is friends with User IDs = 0, 2, 8
User ID=2 is friends with User IDs = 1, 3
User ID=3 is friends with User IDs = 2
User ID=8 is friends with User IDs = 1
Spend time studying the above small example to understand the model. For example, notice that since friendship is a
symmetric relationship the social media networks in this assignment, if user_u is friends with user_v, that means that user_v
is also friends with user_u. Such “duplicate” friendships are not present in the file. In particular each friendship is listed once
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in such way that user_u < user_v
Also note that, while you can assume that user IDs are sorted, you cannot assume that they are consecutive integers
differing by one. For example the user IDs above are: 0,1,2,3,8.
You can also assume that in each file the users are sorted from smallest to largest (in the above example you see that users
appear as: 0 1 1 2). Specifically, friendships of user_u appear before friendships of user_v if and only if user_u < user_v. And also for each user its friends appear sorted, for example for user 1 friendship with friend 2 appears before friendship with friend 4. To complete the assignment you will have to code the following 9 functions. I strongly recommend you code the in the order given below and do not move onto coding a function until you complete all before. The function descriptions, including what they need to do, are given in a5_xxxxxx.py. 1. create_network(file_name) (35 points) This is the most important (and possibly the most difficult) function to solve. The function needs to read a file and return a list of tuples representing the social network from the file. In particular the function returns a list of tuples where each tuple has 2 elements: the first is an integer representing an ID of a user and the second is the list of integers representing his/her friends. In the a5_xxxxxx.py I refer the list that create_network function returns as a 2D-list for friendship network (although one can argue that is is a 3D list). In addition the 2D-list for friendship network that must create_network function returns must be sorted by the ID and a list of friends in each tuple also must be sorted. So for the example above, this function should return the following 2D-list for 2D-list for friendship network: [(0, [1]), (1, [0,2,8]), (2,[1,3]), (3,[2]), (8,[1])] More examples: >>> net1=create_network(“net1.txt”)
>>> net1
[(0, [1, 2, 3]), (1, [0, 4, 6, 7, 9]), (2, [0, 3, 6, 8, 9]), (3, [0, 2, 8, 9]), (4, [1, 6, 7, 8]),
(5, [9]), (6, [1, 2, 4, 8]), (7, [1, 4, 8]), (8, [2, 3, 4, 6, 7]), (9, [1, 2, 3, 5])]
>>> net2=create_network(“net2.txt”)
>>> net2
[(0, [1, 2, 3, 4, 5, 6, 7, 8, 9]), (1, [0, 4, 6, 7, 9]), (2, [0, 3, 6,8, 9]), (3, [0, 2, 8, 9]), (4, [0, 1, 6, 7, 8]),
(5, [0, 9]), (6, [0, 1, 2, 4, 8]), (7, [0, 1, 4, 8]), (8, [0, 2, 3, 4, 6, 7]), (9, [0, 1, 2, 3, 5])]
>>> net3=create_network(“net3.txt”)
>>>
[(0, [1, 2, 3, 4, 5, 6, 7, 8, 9]), (1, [0, 4, 6, 7, 9]), (2, [0, 3, 6,8, 9]), (3, [0, 2, 8, 9]), (4, [0, 1, 6, 7, 8]),
(5, [0, 9]), (6, [0, 1, 2, 4, 8]), (7, [0, 1, 4, 8]), (8, [0, 2, 3, 4, 6, 7]), (9, [0, 1, 2, 3, 5]),
(100, [112]), (112, [100, 114]), (114, [112])]
>>> net4=create_network(“big.txt”)
>>> net4[500:502]
[(500, [348, 353, 354, 355, 361, 363, 368, 373, 374, 376, 378, 382, 388, 391, 392, 396, 400, 402, 404, 408, 409, 410,
412, 414, 416, 417, 421, 423, 428, 431, 438, 439, 444, 445, 450,
452,455, 463, 465, 474, 475, 483, 484,487, 492, 493,
497, 503, 506, 507, 513, 514, 517, 519, 520, 521, 524, 525, 527, 531, 537, 538, 542, 546, 547, 548, 553, 555, 556, 557560, 563, 565, 566, 580, 591, 601, 604, 614, 637, 645, 651, 683]), (501, [198, 348, 364, 393, 399, 441, 476, 564])]
2. getCommonFriends(user1, user2, network) (15 points)
>>> getCommonFriends(3,1,net1)
[0, 9]
>>> getCommonFriends(0,112,net3)
[]
>>> getCommonFriends(217,163,net4)
[0, 100, 119, 150]
3. recommend(user, network) (15 points)
Read the docstrings to understand how this function should work. Understand why the given friends are recommended
in the examples below including why no friend is recommended for 0 in net2 and 112 in net 3.
>>> recommend(6,net1)
7
>>> recommend(4,net2)
2
>>> recommend(0,net2)
3
>>> recommend(114, net3)
100
>>> recommend(112,net3)
>>> recommend(217,net4)
163
4. k_or_more_friends(network, k) (5 points)
>>> k_or_more_friends(net1, 5)
3
>>> k_or_more_friends(net2, 8)
1
>>> k_or_more_friends(net3, 12)
0
>>> k_or_more_friends(net4, 70)
33
5. maximum_num_friends(network) (5 points)
>>> maximum_num_friends(net1)
5
>>> maximum_num_friends(net2)
9
>>> maximum_num_friends(net3)
9
>>> maximum_num_friends(net4)
347
6. people_with_most_friends(network) (5 points)
>>> people_with_most_friends(net1)
[1, 2, 8]
>>> people_with_most_friends(net2)
[0]
>>> people_with_most_friends(net3)
[0]
>>> people_with_most_friends(net4)
[0]
7. average_num_friends(network) (5 points)
>>> average_num_friends(net1)
3.8
>>> average_num_friends(net2)
5.0
>>> average_num_friends(net3)
4.153846153846154
>>> average_num_friends(net4)
19.78
8. knows_everyone(network) (5 points)
>>> knows_everyone(net1)
False
>>> knows_everyone(net2)
True
>>> knows_everyone(net3)
False
>>> knows_everyone(net4)
False
9. get_uid(network) (10 points)
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>>> get_uid(net1)
Enter an integer for a user ID:alsj
That was not an integer. Please try again.
Enter an integer for a user ID: twenty
That was not an integer. Please try again.
Enter an integer for a user ID:9aslj
That was not an integer. Please try again.
Enter an integer for a user ID:100000
That user ID does not exist. Try again.
Enter an integer for a user ID:4.5
That was not an integer. Please try again.
Enter an integer for a user ID: -10
That user ID does not exist. Try again.
Enter an integer for a user ID:-1
That user ID does not exist. Try again.
Enter an integer for a user ID:7
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1.1 Bonus (15 points)
This assignment offers up to 15% bonus. Thus a person for a person who obtained a full bonus Assignment 5 will be worth
8.05% of the final grade. The bonus is available for the maximum of 30-40 students. If there is more candidates for bonus than
that I will pick them at random. In the past, whenever I had bonus there was never more than 30-40 candidates, since in order
for a student to have a chance to get the bonus all of the following needs to happen:
1. She needs to solve correctly getCommonFriends(user1, user2, network) with running time
O(n1 + n2 + log n) were n is the the total number of users in the network, n1 is the number of friends of user1 and n2 is
the number of friends of user2. In other words, n1 =len(user1), n2 =len(user2) and n =len(network).
Note that on a typical network O(n1+n2+log n) is much better than O(n) since a network like Facebook has n roughly 2
billion and the average number of friends per user is 338. Thus the number of operations an O(n) solution would do, would
be in the order of a billion, roughly. While the number of operations an O(num_friends_user1 + num_friends_user2 + log n)
solution would do, would be in the order of, O(338 + 338 + 21), thousand, roughly
Thus O(n) solutions will not be accepted for the bonus.
To determine the running times of Python’s functions on lists you can use this link (although it is not quite correct as it
is amortized, which they incorrectly call average, analysis and not the worst case analysis).
https://wiki.python.org/moin/TimeComplexity
Again you cannot use sets nor dictionaries nor deque nor bisect module.
2. She needs to wait to get her grade for Assignment 5 from TAs. If and only if her grade for create_network and
getCommonFriends functions is 100% that means her solution is correct and thus she is a candidate for bonus.
3. She needs to email the professor with title “Assignment 5 bonus”
4. Finally, when I am computing the final grades of the course, if I see that
a. the student emailed me about the bonus and
b. she got 100% of those two functions and
c. 15% bonus on A5 would make a difference to the final course grade of the student,
then I will invite the student for a zoom interview where she will need to explain her faster solution and the running time
analysis of her solution.
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