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> { // 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:
IllegalArgumentException
if the client calls either addFirst()
or addLast()
with a null
argument.
java.util.NoSuchElementException
if the client calls either removeFirst()
or removeLast
when the deque is empty.
java.util.NoSuchElementException
if the client calls the next()
method in the iterator when there are no more items to return.
UnsupportedOperationException
if the client calls
the remove()
method in the iterator.
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 deque implementation must support each deque operation (including construction) in constant worst-case time. A deque containing n items must use at most 48n + 192 bytes of memory. 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 among items in
the data structure.
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:
IllegalArgumentException
if the client calls
enqueue()
with a null
argument.
java.util.NoSuchElementException
if the client calls either sample()
or
dequeue()
when the randomized queue is empty.
java.util.NoSuchElementException
if the client calls the next()
method in the iterator when there are no more items to return.
UnsupportedOperationException
if the client calls
the remove()
method in the iterator.
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 randomized queue implementation must support each randomized queue operation
(besides creating an iterator) in constant amortized time.
That is, any intermixed 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.
A randomized queue containing n items must use at most
48n + 192 bytes of memory.
Additionally, your iterator implementation must support
operations next()
and hasNext()
in constant worst-case time;
and construction in linear time; you may (and will need to) use a
linear amount of extra memory per iterator.
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.
The running time of Permutation
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 one Deque
or RandomizedQueue
object of maximum size at most k.)
Deliverables.
Submit the programs RandomizedQueue.java
, Deque.java
, and
Permutation.java
, along with a
readme.txt
file,
answering all questions.
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
.
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
.