CS2030 Lab 6-Integer Streams Solution

Topic Coverage
Application of basic Java Streams
Requirements
Java Streams are to be used for the method implementations as specified in this assignment
Task 1
Perfect Numbers
Define the method isPerfect that takes in an integer n and determines if n is a perfect number.
A perfect number is a positive integer that is equal to the sum of its proper divisors. A proper divisor is a positive integer other than the number itself that divides the number evenly (i.e. no remainder).
For example, 6 is the smallest perfect number, because the sum of its proper divisors 1, 2, and 3 is equal to 6. 8 is not a perfect number because 1 + 2 + 4 is not equal to 8. Note that 1 is not a perfect number by definition.
static boolean isPerfect(int n)
The following is a sample run of the program. User input is underlined.
6 true
8 false
Check the format correctness of the output by typing the following Unix command
$ java Main < test1.in | diff - test1.out
Make a copy of your Java programs to the level directory by typing the Unix commands
$ jar cvf stream1.jar *.java
$ mkdir stream1
$ cp *.java stream1
$ cp stream1.jar stream1
Verify your jar archive using
$ jar tvf ~/stream1/stream1.jar

The Tasks
There are several tasks in this assignment. You need to complete ALL the tasks. The tasks pre-supposes familiarity with the primitive type IntStream and hence some method signatures take primitive arrays as arguments. However, if you are familiar with object Streams, you are allowed to change the method parameter type from primitive array to List instead.
In each task, you are to
define a Main class with the main method to handle input and output;
check for output format correctness using the diff utility (see specific level for usage details). Note that only one test case is provided for this; save a copy of all source files into the appropriate level directory (see specific level for usage details).

Task 2
Square Numbers
Define the method isSquare that takes in an integer n and determines if n is a square number.
A perfect square is the square of an integer. Examples are 9 (= 3×3), 4 (= 2×2), and 1 (= 1×1).
static boolean isSquare(int n)
The following is a sample run of the program. User input is underlined.
81 true
80 false
Check the format correctness of the output by typing the following Unix command
$ java Main < test2.in | diff - test2.out
Make a copy of your Java programs to the level directory by typing the Unix commands
$ jar cvf stream2.jar *.java
$ mkdir stream2
$ cp *.java stream2
$ cp stream2.jar stream2
Verify your jar archive using
$ jar tvf ~/stream2/stream2.jar
Task 3
Counting Repeats
Define the method countRepeats that takes in a List of digits 0 to 9 and returns the number of occurrences of adjacent repeated digits.
static long countRepeats(int[] array)
For example,
the array {0, 1, 2, 2, 1, 2, 2, 1, 3, 3, 1} has three occurrences of repeated digits the array {0, 1, 1, 1, 1, 2} has one occurrence
The following is a sample run of the program. User input is underlined.
0 1 2 2 1 2 2 1 3 3 1
^D
Number of occurrences: 3
Check the format correctness of the output by typing the following Unix command
$ java Main < test3.in | diff - test3.out
Make a copy of your Java programs to the level directory by typing the Unix commands
$ jar cvf stream3.jar *.java
$ mkdir stream3
$ cp *.java stream3
$ cp stream3.jar stream3
Verify your jar archive using
$ jar tvf ~/stream3/stream3.jar


Task 4
Finding Variance
Define the method variance that takes in an integer array of elements and returns the variance of the elements. The variance of an array of elements is defined as

where is the mean (or average) of all elements. Note that variance is only valid for an array of two or more elements.
Examples,
variance(IntStream.rangeClosed(1,6).toArray()) returns OptionalDouble[3.5]; variance(IntStream.of().toArray()) returns OptionalDouble.empty variance(IntStream.of(1).toArray()) returns OptionalDouble.empty
The following is a sample run of the program. User input is underlined.
0 1 2 2 1 2 2 1 3 3 1
Variance: OptionalDouble[0.8545454545454545]
^D
Variance: OptionalDouble.empty
1
^D
Variance: OptionalDouble.empty
Check the format correctness of the output by typing the following Unix command
$ java Main < test4.in | diff - test4.out
Make a copy of your Java programs to the level directory by typing the Unix commands
$ jar cvf stream4.jar *.java
$ mkdir stream4
$ cp *.java stream4
$ cp stream4.jar stream4
Verify your jar archive using
$ jar tvf ~/stream4/stream4.jar


Task 5
Prime Factors
Write a method factors with that takes in an integer x and returns a IntStream consisting of the factors of x.
static IntStream factors(int x)
As an example, factors(6) should return the stream of integers 1, 2, 3, 6.
Thereafter, write a method primeFactors that takes in an integer x (> 1) and returns a IntStream consisting of the prime factors of x.
A prime factor is a factor that is a prime number, excluding 1. For instance, prime factors of 6 are 2 and 3.
static IntStream primeFactors(int x)
The following is a sample run of the program. User input is underlined.
6
Prime factors of 6 are: 2 3
12
Prime factors of 6 are: 2 3
731
Prime factors of 731 are: 17 43
Check the format correctness of the output by typing the following Unix command
$ java Main < test5.in | diff - test5.out
Make a copy of your Java programs to the level directory by typing the Unix commands
$ jar cvf stream5.jar *.java
$ mkdir stream5
$ cp *.java stream5
$ cp stream5.jar stream5
Verify your jar archive using
$ jar tvf ~/stream5/stream5.jar