Concurrent and Functional Programming

Task Lists Answers:

#0 · #1 · #2 · #3 · #4 · #5 · #6 · #7 · #8 · #9 · #10 · #11 · #12 · #13

Hey! 👋

So the funny thing about this lecture was that all of these tasks were given at the start of laboratories class and we had 1 hour to write these answers. Obviously, this could lead to increased cortisol levels, accelerated sweating, or the feeling of impending doom, but besides that, that was quite a refreshing experience. Hopefully, these answers to various tasks that I have written could help you relieve some stress and give you mental clarity in any situation that you are currently facing and somehow ended up here.

Regarding the tasks: keep in mind that I had only 1 hour starting from reading what brand-new problem I have to solve, through thinking of a decent solution up to spitting it through keys on keyboards into a .scala or .sc file and then sending the solutions. There are some simple but exhaustive tests for all the tasks and sometimes even comments with explanations. Maybe it could be better, but for your convenience... maybe it is good enough? I hope so!

Cheers and have fun! 🤗

Details of Tasks in Task Lists in a tl;dr

Task List #0 - Introduction

Everything is written in a functional style; recursively using only head & tail.

Tasks:

• #1: Return last element of a list.

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Task List #1 - Functional Programming

Everything is written in a functional style; recursively using only head & tail.

Tasks:

• #1: Return the sum of the whole list.
• #2: Return a pair - first & last element of a list.
• #3: Return a boolean whether the list is sorted or not
• #4: Return merged string based on a given list with a given separator

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Task List #2 - Pattern Matching

Tasks from 1 to 4 are using a pattern matching mechanism & tasks from 1 to 3 have linear complexity with respect to the length of the input list.

Tasks:

• #1: Write a function that takes N first elements of a list.
• #2: Write a function that drops N first elements of a list.
• #3: Write a function that reverses a list.
• #4: Write a function that repeats N times the element where N is an integer in a list.
• #5: Calculate 3rd root of a double with epsilon approximation.

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Task List #3 - List Folding

Tasks:

• #1: Write a function that returns a Boolean whether an element is in a list
  • a) with pattern matching and recursion
  • b) with foldLeft
  • c) with foldRight
• #2: Write a filter function with foldRight.
• #3: Write a function which removes the first found element given in as functional
• #4: Write a function that splits a list in two at given index without double list traversing.

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Task List #4 - Tree & Graph

Tasks:

• #1: Write a function that sums up vertices from Binary Tree
• #2: Write a fold function for Binary Trees
• #3: Write a function that uses foldBT (from Task #2) to sum up the vertices from Binary Tree and another one that creates a list out of vertices from Binary Tree:
  • a) infix
  • b) prefix
  • c) postfix
• #4: Using foldBT create a functional map function
• #4: Write a function to check whether a path between two vertices in a Graph exist

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Task List #5 - Tree & Graph

Tasks:

• #1: Create a class for polymorphic pair. It should have accessors, mutators and toString method.
• #2 a): Extend BankAccount class in which 1$ will be withdrawn for every transaction.
• #2 b): Extend BankAccount class in which 1$ will be withdrawn after 3rd transaction in a given month. Implement Interest logic.
• #3 a): Create an abstract class Animal that has methods for voice, animal type and overridden custom toString. It shall have an unmodifiable name in the constructor
• #3 b): Define public methods for some animals. They should allow creating new instances of animals w/ or w/o name.
• #3 c): Create Test Class for Animals (w/ Vector).

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Task List #6 - Side Effects & Lazy Binary Tree

Tasks:

• #1: Write a whileLoop function (without using computational effects) that takes two arguments: a condition and an expression, and accurately simulates the performance of a while loop (also syntactically). What type (and why) must the arguments and the result of the function be?
• #2: Write the function lrepeat, which for given positive integer ki of the stream Stream (x0, x1, x2, x3, ...) returns a stream where each xi element is repeated k times
• #3 a): Write the function lBreadth, which creates a stream containing all the node values of the lazy binary tree
• #3 b): Write the function lTree: which for a given natural number n constructs an infinite lazy binary tree with root n and two subtrees lTree (2 * n) and lTree (2 * n + 1).

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Task List #7 - Covariant Immutable Queue & Tree Traversing

Tasks:

• #1: Define a general class for a covariant unmodifiable queue represented by two lists.
• #2: Write a breadthBT [A] function: BT [A] => List [A] traversing binary tree in breadth and returning a list of values stored in tree nodes.

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Task List #8 - Cyclic Mutable Queue

Tasks:

• #1 a): Write the class extending the queue as a circular array (all operations are performed by modulo the size of the array)
• #1 b): It's basically the same task, but I did a different implementation as requested on labs.

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Task List #9 - Concurrent Programming

Tasks:

• #1:
  • a): Analyse the program: why the counter value is not as it could be expected to be?
  • b): Fix it with synchronised code
  • c): Fix it using Semaphores.
• #2: Implement method parallel that takes two blocks of arguments as a parameter and executes them simultaneously.
• #2: Implement method periodically that takes the number of repetitions and pause-timer as arguments. The method should make use of daemons.

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Task List #10 - Dining Philosophers & Execution Contexts / Buffers

Tasks:

• #1:
  • a): Rewrite Consumer/Producer classes from Lecture using ArrayBlockingQueue instead BoundedBuffer.
  • b): Create several Consumer-s and Producer-s and investigate.
  • c): Analyse the program: why the counter value is not as it could be expected to be? Fixing the program.
• #2: Dining Philosophers Problem

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Task List #11 - Futures & Promises

Tasks:

• #1: Define a function pairFut[A, B] (fut1: Future[A], fut2: Future[B]): Future[(A, B)] = ???
  • a) Using zip method
  • b) Using for
• #2: Add exists method to Future[T] type
  • a) Using promise
  • b) Without promise
• #3: Count the amount of words in all files in a given directory

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Task List #12 - Client-Server Game

Tasks:

• #1: Create an actor Server that generates a random number and awaits signals from clients with guess messages.
• #2: Create actor Client with params name, server reference, upper guess number limit that makes optimal number guesses and interacts with Server.
• #3: Write a complete application that creates a server instance and at least two clients that are guessing the numbers. Make a start signal from the main.

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Task List #13 - Emitting Events

Tasks:

• #1: Define two observable objects, one of which emits an event every 5 and the other one emits an event every 12 second but both of them do not emit anything when time is multiple of 30 seconds. One of them should use merge method.
• #2: Define one observable object that emits an event every 5 and 12 second but not when time is multiple of 30 seconds. Use filter method.