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日期:2021-10-24 09:00

CS 170: Introduction to Computer Science I – Fall 2021
Homework Assignment #3
Due by Tuesday, October 26, 2021 at 2:00 pm
Submission instructions br>Submit your assignment through the QTest system, using exam ID: CS170.hw3.
No email submissions are accepted. No late submissions are accepted.
General instructions and hints
In those problems asking you to write a method, always call the method several times to test that it works properly
with a variety of different values for the parameters. Test it on more examples than the ones shown in this
handout. Even if the problem asks you for just one method, you can always write additional helper methods to
simplify and organize your code. Make sure you write comments to explain your code.
Comment requirements: Always comment the top of each method (what the method does, the meaning of
the input parameters, the meaning of the output value). Write comments within the methods to explain the
strategy you are using to solve the problem, and to clarify blocks of code that may be difficult to
understand.
Problem 1: Mid semester survey (2 points)
Go to the following website and complete the survey.
https://docs.google.com/forms/d/e/1FAIpQLScpQ_lDvmdLjSCtozLDFBE-
DnGCivK2vUkverKdhWBtxP85tQ/viewform
The answers to the survey will not be graded: you will receive credit just for completing it.
Problem 1 rubric:
2 points for completing the survey.
Problem 2: Average length (5 points)
Write a method named avgLength which takes an array of Strings as an input parameter and returns a double.
The method should calculate and return the average length of all the strings in the array.
Examples:
avgLength(new String[]{"Hello", "Q"}) returns 3.0
avgLength(new String[]{}) returns 0.0
avgLength(new String[]{"Hello", "Goodbye"}) returns 6.0
Rubric:
programs that do not compile get zero points
+5 correct implementation (up to 4 points for a partially correct solution. Zero points if the solution is far
from correct)
-1 incorrect method signature (method name, number of parameters, and types of parameters)
-1 if there are no test cases
-1 if there are no comments, insufficient comments, or bad usage of comments
1
Problem 3: Angle (5 points)
Write a method named angle(double[] x, double[] y) that takes two arrays of doubles, and returns
the angle (in degrees, 0.0 <= angle < 180.0) between the two arrays. To calculate the angle, you can use the
geometric definition of the dot product between the arrays:
https://en.wikipedia.org/wiki/Dot_product#Geometric_definition
If one array is shorter than the other, treat the missing elements as zeros. If the norm of any of the two arrays is
zero, the angle is zero.
Examples:
angle(new double[]{1, 2, 3}, new double[]{4, 5}) returns 54.243...
angle(new double[]{0}, new double[]{4, 5}) returns 0.0
angle(new double[]{3, 0}, new double[]{0, 3}) returns 90.0
angle(new double[]{2, 1, 5, -4}, new double[]{6, 3, 15, -12}) returns 0.0
Rubric:
programs that do not compile get zero points
+5 correct implementation (up to 4 points for a partially correct solution. Zero points if the solution is far
from correct)
-1 incorrect method signature (method name, number of parameters, and types of parameters)
-1 if there are no test cases
-1 if there are no comments, insufficient comments, or bad usage of comments
Problem 4: Reverse copy (5 points)
Write a method named reverseCopy that takes an array of integers and returns a copy of the array with its
elements in reverse order.
Example:
reverseCopy(new int[]{1, 2, 3}) returns {3, 2, 1}
Rubric:
programs that do not compile get zero points
+5 correct implementation (up to 4 points for a partially correct solution. Zero points if the solution is far
from correct)
-1 incorrect method signature (method name, number of parameters, and types of parameters)
-1 if there are no test cases
-1 if there are no comments, insufficient comments, or bad usage of comments
Problem 5: Reverse in place (5 points)
Write a method named reverse that takes an array of integers and reverses the order of its elements. The
original array is modified and the method doesn’t return anything.
Rubric:
programs that do not compile get zero points
+5 correct implementation (up to 4 points for a partially correct solution. Zero points if the solution is far
from correct)
-1 incorrect method signature (method name, number of parameters, and types of parameters)
-1 if there are no test cases
2
-1 if there are no comments, insufficient comments, or bad usage of comments
Problem 6: Tally vowels (5 points)
Write a method named tally that takes a String and returns an array of 5 integers containing the frequencies
of the 5 vowels (a, e, i, o, u) in the input string. Uppercase and lowercase vowels are counted in the same way.
Example:
tally("HEY! Apples and bananas!") will return: {5, 2, 0, 0, 0}
Rubric:
programs that do not compile get zero points
+5 correct implementation (up to 4 points for a partially correct solution. Zero points if the solution is far
from correct)
-1 incorrect method signature (method name, number of parameters, and types of parameters)
-1 if there are no test cases
-1 if there are no comments, insufficient comments, or bad usage of comments
Problem 7: Student averages (5 points)
Write a method named studentAverages which takes a 2D array of integers as input. Each column in the
2D array is an assignment and each row is composed of grades for a particular student (see below for an
example). Your method should return an array of doubles representing the grades for each student. You may
assume each assignment is scored out of 100 points.
Quiz 1 Quiz 2 Quiz 3
Maggie Simpson 50 100 0
Lisa Simpson 100 100 80
studentAverages(new int[][]{{50,100,0}, {100,100,80}}) returns {50.0, 93.33333}
Rubric:
programs that do not compile get zero points
+5 correct implementation (up to 4 points for a partially correct solution. Zero points if the solution is far
from correct)
-1 incorrect method signature (method name, number of parameters, and types of parameters)
-1 if there are no test cases
-1 if there are no comments, insufficient comments, or bad usage of comments
Problem 8: Swear word filter (8 points)
Write a method named swearFilter(String text, String[] swear) that takes two parameters: a
String containing some text, and an array of Strings containing a list of "swear words". Your method will return a
String containing the text contained in the first String, where each "swear word" is replaced by its first character,
followed by a number of stars equal to its number of characters minus two, followed by its last character. For
example, if the swear words are "duck", "ship", and "whole", and the text contains the following story:
A duck was sailing on a ship shipping whole wheat bread. Duck that SHIP!!!
Your method would return:
3
A d**k was sailing on a s**p s**pping w***e wheat bread. D**k that S**P!!!
Your method should recognize both uppercase and lowercase characters in a swear word. If a swear word is less
than 3 characters long, the filter has no effect for that swear word. You cannot use any pre-made search/replace
methods such as indexOf, replaceAll, etc.
Rubric:
programs that do not compile get zero points
+8 correct implementation (up to 7 points for a partially correct solution. Zero points if the solution is far
from correct)
-2 for swear-word matching being case-sensitive
-2 for not maintaining original upper/lower-case
-2 for not matching strings that contain swear words as substrings
-1 incorrect method signature (method name, number of parameters, and types of parameters)
-1 if there are no test cases
-1 if there are no comments, insufficient comments, or bad usage of comments
Bonus points: Early submission
If you submit the entire homework no later than 48 hours before the deadline, and the total score on the rest of this
homework assignment is at least 20 points, you will receive 2 bonus points. The bonus points will be added to the
total score of this homework assignment.
Good luck and have fun!

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