Queues

• Checklist
• Project
• Submit

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 collection. Create a generic data type Deque that implements the following API:

public class Deque<Item> implements Iterable<Item> {

    // construct an empty deque
    public Deque()

    // is the deque empty?
    public boolean isEmpty()

    // return the number of items on the deque
    public int size()

    // add the item to the front
    public void addFirst(Item item)

    // add the item to the back
    public void addLast(Item item)

    // remove and return the item from the front
    public Item removeFirst()

    // remove and return the item from the back
    public Item removeLast()

    // return an iterator over items in order from front to back
    public Iterator<Item> iterator()

    // unit testing (required)
    public static void main(String[] args)

}

Corner cases.  Throw the specified exception for the following corner cases:

• Throw an IllegalArgumentException if the client calls either addFirst() or addLast() with a null argument.
• Throw a java.util.NoSuchElementException if the client calls either removeFirst() or removeLast when the deque is empty.
• Throw a java.util.NoSuchElementException if the client calls the next() method in the iterator when there are no more items to return.

Unit testing.  Your main() method must call directly every public constructor and method to help verify that they work as prescribed (e.g., by printing results to standard output).

Performance requirements.  Your implementation must achieve the following worst-case performance requirements:

• A deque containing n items must use at most 48n + 192 bytes of memory, not including the memory for the items themselves.
• Each deque operation (including construction) must take constant time.
• Each iterator operation (including construction) must take constant time.

Randomized queue. A randomized queue is similar to a stack or queue, except that the item removed is chosen uniformly at random among items in the collection. Create a generic data type RandomizedQueue that implements the following API:

public class RandomizedQueue<Item> implements Iterable<Item> {

    // construct an empty randomized queue
    public RandomizedQueue()

    // is the randomized queue empty?
    public boolean isEmpty()

    // return the number of items on the randomized queue
    public int size()

    // add the item
    public void enqueue(Item item)

    // remove and return a random item
    public Item dequeue()

    // return a random item (but do not remove it)
    public Item sample()

    // return an independent iterator over items in random order
    public Iterator<Item> iterator()

    // unit testing (required)
    public static void main(String[] args)

}

Iterator.  Each iterator must return the items in uniformly random order. 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 the specified exception for the following corner cases:

• Throw an IllegalArgumentException if the client calls enqueue() with a null argument.
• Throw a java.util.NoSuchElementException if the client calls either sample() or dequeue() when the randomized queue is empty.
• Throw a java.util.NoSuchElementException if the client calls the next() method in the iterator when there are no more items to return.

Unit testing.  Your main() method must call directly every public constructor and method to verify that they work as prescribed (e.g., by printing results to standard output).

Performance requirements.  Your implementation must achieve the following worst-case performance requirements:

• A randomized queue containing n items must use at most 48n + 192 bytes of memory, not including the memory for the items themselves.
• Each randomized queue operation (besides creating an iterator) must take constant amortized time. That is, starting from an empty randomized queue, any intermixed sequence of m such operations must take \(\Theta(m)\) time in the worst case.
• An iterator over n items must at use at most 8n + 72 bytes of memory.
• Constructing an iterator must take \(\Theta(n)\) time; the next() and hasNext() operations must take constant time.

Client. Write a client program Permutation.java that takes an integer k as a command-line argument; reads a sequence of strings from standard input using StdIn.readString(); and prints exactly k of them, uniformly at random. Print each item from the sequence at most once.

~/Desktop/queues> more distinct.txt A B C D E F G H I ~/Desktop/queues> java-algs4 Permutation 3 < distinct.txt C G A ~/Desktop/queues> java-algs4 Permutation 3 < distinct.txt E F G

~/Desktop/queues> more duplicates.txt AA BB BB BB BB BB CC CC ~/Desktop/queues> java-algs4 Permutation 8 < duplicates.txt BB AA BB CC BB BB CC BB

Your program must implement the following API:

public class Permutation {
   public static void main(String[] args)
}

Command-line argument.  You may assume that 0 ≤ k ≤ n, where n is the number of string on standard input. Note that you are not given n.

Performance requirements.  Your implementation must achieve the following worst-case performance requirements:

• The running time of Permutation must be 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.
• For an extra challenge (and a small amount of extra credit), use only a constant amount of memory plus either one Deque or RandomizedQueue object of maximum size at most k.

Submission. Submit the programs RandomizedQueue.java, Deque.java, and Permutation.java. Your submission may not call library functions except those in StdIn, StdOut, StdRandom, java.lang, java.util.Iterator, and java.util.NoSuchElementException. In particular, do not use either java.util.LinkedList or java.util.ArrayList. Finally, submit readme.txt and acknowledgments.txt files and answer the questions.

Grading.

file	points
Deque.java	15
RandomizedQueue.java	15
Permutation.java	5
readme.txt	5
	40

Reminder: You can lose up to 4 points for poor style and up to 4 points for inadequate unit testing.

Extra credit: You can earn 2 points of extra credit for conserving memory in Permutation.java.