Project 2 (Deques and Randomized Queues) Solution

The purpose of this project is to implement elementary data structures using arrays and linked lists, and to introduce you to generics and iterators.




Problem 1. (Deque) A double-ended queue or deque (pronounced \deck") is a generalization of a stack and a queue that supports adding and removing items from either the front or the back of the data structure. Create a generic iterable data type LinkedDeque<Item in LinkedDeque.java that uses a linked list to implement the following deque API:




method
description




LinkedDeque()
construct an empty deque
boolean isEmpty()
is the deque empty?
int size()
the number of items on the deque
void addFirst(Item item)
add item to the front of the deque
void addLast(Item item)
add item to the end of the deque
Item removeFirst()
remove and return the item from the front of the deque
Item removeLast()
remove and return the item from the end of the deque



Iterator<Item iterator() an iterator over items in the deque in order from front to end




String toString() a string representation of the deque




Corner cases. Throw a java.lang.NullPointerException if the client attempts to add a null item;




throw a java.util.NoSuchElementException if the client attempts to remove an item from an empty deque; throw a java.lang.UnsupportedOperationException if the client calls the remove() method in the iterator; throw a java.util.NoSuchElementException if the client calls the next() method in the iterator and there are no more items to return.




Performance requirements. Your deque implementation must support each deque operation (including construction) in constant worst-case time and use space proportional to linear in the number of items currently in the deque. Additionally, your iterator implementation must support each operation (including construction) in constant worst-case time.







java L i n k e d D e q u e false



(364 c h a r a c t e r s ) There is grandeur in this view of life , with its several powers , having been o r i g i n a l l y




breathed into a few forms or into one ; and that , whilst this
planet has
gone cycling
on a cc or d in g to
the fixed law of gravity , from so simple a be g in ni n g endless
forms
most
b ea u ti fu l and
most w on d er fu l






have been , and are being , evolved . ~ Charles Darwin , The Origin of
Species












true
























Problem 2. (Random Queue) A random queue is similar to a stack or queue, except that the item removed is chosen uniformly at random from items in the data structure. Create a generic iterable data type ResizingArrayRandomQueue<Item in ResizingArrayRandomQueue.java that uses a resizing array to implement the following random queue API:




method
description




ResizingArrayRandomQueue()
construct an empty queue
boolean isEmpty()
is the queue empty?
int size()
the number of items on the queue
void enqueue(Item item)
add item to the queue
Item dequeue()
remove and return a random item from the queue
Item sample()
return a random item from the queue, but do not remove it



Iterator<Item iterator() an independent iterator over items in the queue in random order




String toString() a string representation of the queue







The order of two or more iterators to the same randomized queue must be mutually independent; each iterator must maintain its own random order.




Corner cases. Throw a java.lang.NullPointerException if the client attempts to add a null item;




throw a java.util.NoSuchElementException if the client attempts to sample or dequeue an item from an empty randomized







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CS210 Project 2 (Deques and Randomized Queues) Swami Iyer










queue; throw a java.lang.UnsupportedOperationException if the client calls the remove() method in the iterator; throw a java.util.NoSuchElementException if the client calls the next() method in the iterator and there are no more items to return.




Performance requirements. Your randomized queue implementation must support each randomized queue operation (besides creating an iterator) in constant amortized time and use space proportional to linear in the number of items currently in the queue. That is, any sequence of M randomized queue operations (starting from an empty queue) must take at most cM steps in the worst case, for some constant c. Additionally, your iterator implementation must support next() and hasNext() in constant worst-case time and construction in linear time; you may use a linear amount of extra memory per iterator.







$ java R e s i z i n g A r r a y R a n d o m Q u e u e




12345678910




ctrl -d 55 0 55
true










Problem 3. (Subset) Write a client program Subset.java that takes a command-line integer k, reads in a sequence of strings from standard input using StdIn.readString(), and prints out exactly k of them, uniformly at random. Each item from the sequence can be printed out at most once. You may assume that 0 k N, where N is the number of strings on standard input. The running time of the program must be linear in the size of the input. You may use only a constant amount of memory plus either one LinkedDeque or ResizingArrayRandomQueue object of maximum size at most N.







$ java Subset 3




ABCDEFGHI




ctrl -d



G I E

$ java Subset 3




ABCDEFGHI




ctrl -d



F D E

$ java Subset 8




AA BB BB BB BB BB CC CC




ctrl -d



BB CC AA BB BB BB CC BB







Files to Submit




LinkedDeque.java



ResizingArrayRandomQueue.java



Subset.java



report.txt





















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CS210 Project 2 (Deques and Randomized Queues) Swami Iyer













Before you submit:




Make sure your programs meet the input and output speci cations by running the following command on the terminal:







$ python3 r un _ te st s . py -v [ < problems ]




where the optional argument <problems lists the problems (Problem1, Problem2, etc.) you want to test, separated by spaces; all the problems are tested if no argument is given.




Make sure your programs meet the style requirements by running the following command on the terminal:







$ c h e c k _ s t y l e < program




where <program is the .java le whose style you want to check.




Make sure your report isn’t too verbose, doesn’t contain lines that exceed 80 characters, and doesn’t contain spelling/grammatical mistakes
















Acknowledgements This project is an adaptation of the Deques and Randomized Queues assignment developed at Princeton University by Kevin Wayne.




























































































































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