关于前端:CSCI2110-难点讲解

CSCI2110
Assignment 3
Instructor: Alex Brodsky
Due: 12:00 noon, Monday, February 25, 2019
The purpose of this assignment is to get you to use recursion, lists, and (possibly) stacks
in a useful way and further improve your programming skills. As discussed in class and the
first tutorial, for each problem you will be provided with a description of the problem and
a set of tests. These tests can be run on the submission system (Mimir) or on the unix
server for this course. You can also use these tests on your own computer as illustrated in
the first tutorial. Your code must compile. If it does not compile, you will receive a 0 on
the assignment.
Background: JSON
JSON, the (JavaScript Object Notation) is a widely-used encoding format that makes is easy
to exchange data. JSON is a text-based (human readable) format, which makes it ideal for
many applications as well as easy to debug. For this assignment, you will need to research
the JSON format on the web. For example: https://www.json.org. A brief summary is
provided here, but you are encouraged to do more in-depth research.
JSON encodes data using objects, arrays, and primitive values. A JSON object is encoded
as zero or more key-value pairs, where the key is a string and a value can be an object, an
array, a string, a number, true, false, or null. A string is any piece of text enclosed in
double quotes, e.g., “Hello World” and a number is either an integer or a decimal value,
e.g., 42 and 3.14. Objects begin with an left brace ({), contain zero or more key-value pairs,
and end with a right brace (}), e.g.,
{
“subject code” : “CSCI”,
“course number” : 2110,
“pre-reqs” : [
“CSCI 1110”,
“CSCI 1101”
],
“exclusions” : null,
“core” : true,
“textbook” : {
“author” : “S. Venugopal”,
“title” : “Data Structures Outside In with Java”,
“publisher” : Prentice Hall”,
“year” : 2007,
“ISBN-10” : “0-13-198619-8”
}
}
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CSCI2110 Winter 2019 Assignment 3
In an object, key-value pairs are denoted key : value and multiple key-value pairs are separated
by commas (,). In JSON, an array is a sequence of values of any kind. An array
begins with a left square bracket ([), has zero or more values, separated by commas, and
ends with a right square bracket (]). In the example above the array contains two strings.
If you are not not clear on the structure of JSON, your first task is to review a JSON
tutorial, such as the one here: https://www.tutorialspoint.co…
Problem: JSON Object Equality
Determining if two JSON objects are equal is a common and useful operation. Two JSON
objects are equal if they have the same set of key-value pairs (not necessarily in the same
order), where for each key, the values are equal. In the case of primitive values such as
strings, numbers, true, false, and null, two values are equal if they are the same. In the
case of arrays, two arrays are equal if both arrays have the same number of elements and
they are pairwise equal. I.e., for each array element, the values stored in both arrays are
equal For example, the following two figures are examples of equal and unequal objects.
{
“subject code” : “CSCI”,
“course number” : 2110,
“pre-reqs” : [
“CSCI 1110”,
“CSCI 1101”
],
“exclusions” : null,
“core” : true
}
{
“core” : true,
“course number” : 2110,
“exclusions” : null,
“pre-reqs” : [
“CSCI 1110”,
“CSCI 1101”
],
“subject code” : “CSCI”
}
Figure 1: These JSON objects are equal.
{
“subject code” : “CSCI”,
“course number” : 2110,
“pre-reqs” : [
“CSCI 1110”,
“CSCI 1101”
],
“exclusions” : null,
“core” : true
}
{
“subject code” : “CSCI”,
“course number” : 2110,
“pre-reqs” : [
“CSCI 1101”
“CSCI 1110”,
],
“exclusions” : null,
“core” : true
}
Figure 2: These JSON objects are not equal, because the arrays are not equal.
Your task is to create a program to determine if two JSON objects are equal.
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CSCI2110 Winter 2019 Assignment 3
Write a program called JSim.java that reads in two JSON objects from the console and
determines if they are the equal. Your JSim.java program must contain the main() method
where your program starts running.
Input
The input consists of two JSON objects, one after the other. The input is via the console
(System.in). You may assume that there will be no error in the input.
Reading Input with JSONScanner
The provided JSONScanner class can be used to read in the JSON objects from the console.
This class has a next() method, just like the standard Scanner class. But, instead of
returning the next word in the input, the next() method of the JSONScanner class returns
the next token in the input. A token is one of
token description or example token description or example
{left brace string “Hello World”
} right brace number 42 or 3.14
[left square bracket true
] right square bracket false
: colon null
, comma
The use of JSONScanner class is similar to the Scanner class. First, instantiate an object
from the class, passing in System.in. Then, repeatedly call next() on this object to get
one token after the other (see example below). The hasNext() method is used to check if
another token is available.
public void main(String [] args) {
JSONScanner scanner = new JSDNScanner(System.in);
…
String token = scanner.next();
…
Processing
The input will contain exactly two JSON objects, one after the other.
Two objects are equal if they have the same set of key-value pairs, which may be in
different orders. Two arrays are equal if they are of the same size and are pair-wise equal.
Otherwise, two values are equal if they are the same.
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CSCI2110 Winter 2019 Assignment 3
An object is said to be in sorted form if the key-value pairs are in sorted (alphabetical)
order and all objects inside the object are also in sorted form. For example, in Figure 1, the
object on the left is not in sorted form, while the object on the right is in sorted form.
Output
If the two objects are equal your program should output one of the objects in sorted form
(formatted as described below), followed by
The objects are equal.
If the two objects are not equal your program should output both objects in sorted form
(formatted as described below), followed by
The objects are not equal.
Object Output Format
When outputting an object, the left and right braces should be on separate lines, with the
key-value pairs indented two spaces. There should be single spaces between the key, the
colon, and the value. If the value is an object or an array, the left brace or bracket should
be on the same line. All the key-value pairs or values should be indented two more spaces.
The right brace or bracket should be on separate line, with the same indentation as the keyvalue
pair. A comma separating key-value pairs in an object or values in an array should
immediately follow the key-value pair or value. Please see Figures 1 and 2 for examples.
Examples
Sample Input Sample Output
{
“subject code” : “CSCI”,
“course number” : 1110,
“pre-reqs” : [
],
“core” : true
}
{
“subject code” : “CSCI”,
“course number” : 1110,
“core” : true,
“pre-reqs” : [
]
}
{
“core” : true,
“course number” : 1110,
“pre-reqs” : [
],
“subject code” : “CSCI”
}
The objects are equal.
4
CSCI2110 Winter 2019 Assignment 3
Sample Input Sample Output
{
“subject code” : “CSCI”,
“course number” : 1110,
“pre-requisies” : [
],
“exclusions” : null,
“core” : true
}
{
“subject code” : “CSCI”,
“course number” : 1110,
“core” : true,
“pre-reqs” : [
],
“exclusions” : null
}
{
“core” : true,
“course number” : 1110,
“exclusions” : null,
“pre-requisies” : [
],
“subject code” : “CSCI”
}
{
“core” : true,
“course number” : 1110,
“exclusions” : null,
“pre-reqs” : [
],
“subject code” : “CSCI”
}
The objects are not equal.
Hints and Suggestions
You will either need to use recursion or a stack (or both) to solve this problem.
Java has both stacks (java.utils.Stack) and lists (java.utils.ArrayList) built in.
As well as binary search (java.utils.Arrays).
The sample solution uses a 2-pass algorithm. The first pass reads in the two JSON
objects and stores them. This can be done either iteratively with a stack or recursively.
The second pass determines if the two objects are the same. This is easier to do
recursively. The third pass prints out the first or both objects, and is also easier to do
recursively. Note: The solution cannot be done in a single pass.
There is not a lot of code to write. The sample solution is under 170 lines of code.
Your code must compile. If it does not compile, you will receive a 0 on the assignment.
Your code must be well commented and indented. Please see the Assignments section
for this course on Brightspace for Code Style Guidelines.
You may assume that all input will be correct.
Be sure to test your programs using the provided tests or with Mimir.
What to Hand In
Submit the source files for your program via Mimir as described in the first tutorial. A link
to Mimir is available on Brightspace. At least one of the submitted files must be JSim.java,
which is where the main program starts to run. If you have more than one Java file to
submit, place them all in a zip file and submit that.
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CSCI2110 Winter 2019 Assignment 3
Grading
The assignment will be graded based on three criteria:
Functionality“Does it work according to specifications?”. This is determined in an automated
fashion by running your program on a number of inputs and ensuring that the
outputs match the expected outputs. The score is determined based on the number
of tests that your program passes. So, if your program passes t
T
tests, you will receive
that proportion of the marks.
Quality of Solution“Is it a good solution?”This considers whether the solution is correct,
efficient, covers boundary conditions, does not have any obvious bugs, etc. This is
determined by visual inspection of the code. Initially full marks are given to each
solution and marks are deducted based on faults found in the solution.
Code Clarity“Is it well written?”This considers whether the solution is properly formatted,
well documented, and follows coding style guidelines.
If your program does not compile, it is considered non-functional and of extremely poor
quality, meaning you will receive 0 for the solution.
Marks
Functionality 20
Quality of Solution 20
Code Clarity 10
Total 50
Table 1: Marking scheme for Assignment 3

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