NYU, of Engineering
CS-UY 1134 Data Structures and Algorithms — Spring 2023
Homework #1
Due by Wednesday 2/8, 11:59pm
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Submission instructions:
1. For this assignment, you should turn in 6 files: • A ‘.pdf’ file for the first question.
Name your file: ‘YourNetID_hw1_q1.pdf’
• 5 ‘.py’ files, one for each question 2-6. Name your files:
‘YourNetID_hw1_q2.py’ and ‘YourNetID_hw1_q3.py’, etc. Note: your netID follows an abc123 pattern, not N12345678.
2. You should submit your homework via Gradescope. For Gradescope’s autograding feature to work:
a. Name all classes, functions and methods exactly as they are in the
assignment specifications.
b. Make sure there are no print statements in your code. If you have tester
code, please put it in a “main” function and do not call it.
Question 1:
Draw the memory image for evaluating the following code: >>> lst1 = [1, 2, 3]
>>> lst2 = [lst1 for i in range(3)]
>>> lst2[0][0] = 10
>>> print(lst2)
Question 2:
a. Write a function def shift(lst, k)that is given a list of N numbers, and
some positive integer k (where k
For a detailed explanation of this implementation as well as of the syntax of operator overloading that is used here, please read sections 2.3.2 and 2.3.3 in the textbook (pages 74-78).
class Vector:
def __init__(self, d):
self.coords = [0]*d def __len__(self):
return len(self.coords) def __getitem__(self, j):
return self.coords[j]
def __setitem__(self, j, val):
self.coords[j] = val
def __add__(self, other):
if (len(self) != len(other)):
raise ValueError(”dimensions must agree”) result = Vector(len(self))
for j in range(len(self)):
result[j] = self[j] + other[j] return result
def __eq__(self, other):
return self.coords == other.coords
def __ne__(self, other):
return not (self == other)
def __str__(self):
return ’<’+ str(self.coords)[1:−1] + ’>’
def __repr__(self):
return str(self)
a. The Vector class provides a constructor that takes an integer d, and produces a d-dimensional vector with all coordinates equal to 0. Another convenient form for creating a new vector would be to send the constructor a parameter that is some iterable object representing a sequence of numbers, and to create a vector with dimension equal to the length of that sequence and coordinates equal to the sequence values. For example, Vector([4, 7, 5]) would produce a three- dimensional vector with coordinates <4, 7, 5>.
Modify the constructor so that either of these forms is acceptable; that is, if a single integer is sent, it produces a vector of that dimension with all zeros, but if a sequence of numbers is provided, it produces a vector with coordinates based on that sequence.
Hint: use run-time type checking (the isinstance function) to support both syntaxes.
b. Implementthe__sub__methodfortheVectorclass,sothattheexpression u−v returns a new vector instance representing the difference between two vectors.
c. Implement the __neg__ method for the Vector class, so that the expression −v returns a new vector instance whose coordinates are all the negated values of the respective coordinates of v.
d. Implementthe__mul__methodfortheVectorclass,sothattheexpression v*3 returns a new vector with coordinates that are 3 times the respective coordinates of v.
e. Section (d) asks for an implementation of __mul__, for the Vector class, to provide support for the syntax v*3.
Implement the __rmul__ method, to provide additional support for syntax 3*v.
f. There two kinds of multiplication related to vectors:
1. Scalar product – multiplying a vector by a number (a scalar), as described
and implemented in section (d).
For example, if v = <1, 2, 3>, then v*5 would be <5, 10, 15>.
2. Dot product – multiplying a vector by another vector. In this kind of
multiplication if v =
For example, if v = <1, 2, 3> and u = <4, 5, 6>, then v*u would be 32 (1*4+2*5+3*6=32).
Modify your implementation of the __mul__ method so it will support both
kinds of multiplication. That is, when the user will multiply a vector by a number it will calculate the scalar product and when the user multiplies a vector by another vector, their dot product will be calculated.
After implementing sections (a)-(f), you should expect the following behavior:
>>> v1 = Vector(5)
>>> v1[1] = 10
>>> v1[−1] = 10
>>> print(v1)
<0, 10, 0, 0, 10>
>>> v2 = Vector([2, 4, 6, 8, 10])
>>> print(v2)
<2, 4, 6, 8, 10>
>>> u1 = v1 + v2
>>> print(u1)
<2, 14, 6, 8, 20>
>>> u2 = -v2
>>> print(u2)
<-2, -4, -6, -8, -10>
>>> u3 = 3 * v2
>>> print(u3)
<6, 12, 18, 24, 30>
>>> u4 = v2 * 3
>>> print(u4)
<6, 12, 18, 24, 30>
>>> u5 = v1 * v2
>>> print(u5)
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