Assignment 2: Randomized Queues and Deques

Write a generic data type for a deque and a randomized queue. The goal of this assignment is to implement elementary data
structures using arrays and linked lists, and to introduce you to generics and iterators.
Dequeue. 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 data type Deque that implements the
following API:
public class Deque<Item implements Iterable<Item {
public Deque() // construct an empty deque
public boolean isEmpty() // is the deque empty?
public int size() // return the number of items on the deque
public void addFirst(Item item) // add the item to the front
public void addLast(Item item) // add the item to the end
public Item removeFirst() // remove and return the item from the front
public Item removeLast() // remove and return the item from the end
public Iterator<Item iterator() // return an iterator over items in order from front to end
public static void main(String[] args) // unit testing
}
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 in constant worst-case time and use
space proportional to the number of items currently in the deque. Additionally, your iterator implementation must support each
operation (including construction) in constant worst-case time.
Randomized queue. A randomized 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 data type RandomizedQueue that implements the following API:
public class RandomizedQueue<Item implements Iterable<Item {
public RandomizedQueue() // construct an empty randomized queue
public boolean isEmpty() // is the queue empty?
public int size() // return the number of items on the queue
public void enqueue(Item item) // add the item
public Item dequeue() // remove and return a random item
public Item sample() // return (but do not remove) a random item
public Iterator<Item iterator() // return an independent iterator over items in random order
public static void main(String[] args) // unit testing
}
Corner cases. The order of two or more iterators to the same randomized queue must be mutually independent; each iterator must
maintain its own random order. 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 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 the number of items currently in the queue. That is,
any sequence of M randomized queue operations (starting from an empty queue) should take at most cM steps in the worst case, for
some constant c. Additionally, your iterator implementation must support operations next() and hasNext() in constant worst-case
time; and construction in linear time; you may use a linear amount of extra memory per iterator.
Subset client. Write a client program Subset.java that takes a command-line integer k; reads in a sequence of N 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 string on standard input.
% echo A B C D E F G H I | java Subset 3 % echo AA BB BB BB BB BB CC CC | java Subset 8
C BB
G AA
A BB
CC
% echo A B C D E F G H I | java Subset 3 BB
E BB
F CC
G BB
The running time of Subset must be linear in the size of the input. You may use only a constant amount of memory plus either one
Deque or RandomizedQueue object of maximum size at most N, where N is the number of strings on standard input. (For an extra
challenge, use only one Deque or RandomizedQueue object of maximum size at most k.) It should have the following API.public class Subset {
public static void main(String[] args)
}
Deliverables. Submit only Deque.java, RandomizedQueue.java, and Subset.java. We will supply stdlib.jar. You may not
call any library functions other than those in stdlib.jar, java.lang, java.util.Iterator, and
java.util.NoSuchElementException.