edu.princeton.cs.algs4

Class IndexMaxPQ<Key extends Comparable<Key>>

Object

edu.princeton.cs.algs4.IndexMaxPQ<Key>

Type Parameters:

Key - the generic type of key on this priority queue

All Implemented Interfaces:

Iterable<Integer>

public class IndexMaxPQ<Key extends Comparable<Key>>
extends Object
implements Iterable<Integer>

The IndexMaxPQ class represents an indexed priority queue of generic keys. It supports the usual insert and delete-the-maximum operations, along with delete and change-the-key methods. In order to let the client refer to items on the priority queue, an integer between 0 and maxN - 1 is associated with each key—the client uses this integer to specify which key to delete or change. It also supports methods for peeking at a maximum key, testing if the priority queue is empty, and iterating through the keys.

This implementation uses a binary heap along with an array to associate keys with integers in the given range. The insert, delete-the-maximum, delete, change-key, decrease-key, and increase-key operations take Θ(log n) time in the worst case, where n is the number of elements in the priority queue. Construction takes time proportional to the specified capacity.

For additional documentation, see Section 2.4 of Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne.

Author:

Robert Sedgewick, Kevin Wayne

Constructor Summary

Constructors

Constructor and Description
IndexMaxPQ(int maxN) Initializes an empty indexed priority queue with indices between 0 and maxN - 1.

Method Summary

Modifier and Type	Method and Description
void	change(int i, Key key) Deprecated. Replaced by changeKey(int, Key).
void	changeKey(int i, Key key) Change the key associated with index i to the specified value.
boolean	contains(int i) Is i an index on this priority queue?
void	decreaseKey(int i, Key key) Decrease the key associated with index i to the specified value.
void	delete(int i) Remove the key on the priority queue associated with index i.
int	delMax() Removes a maximum key and returns its associated index.
void	increaseKey(int i, Key key) Increase the key associated with index i to the specified value.
void	insert(int i, Key key) Associate key with index i.
boolean	isEmpty() Returns true if this priority queue is empty.
Iterator<Integer>	iterator() Returns an iterator that iterates over the keys on the priority queue in descending order.
Key	keyOf(int i) Returns the key associated with index i.
static void	main(String[] args) Unit tests the IndexMaxPQ data type.
int	maxIndex() Returns an index associated with a maximum key.
Key	maxKey() Returns a maximum key.
int	size() Returns the number of keys on this priority queue.

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface Iterable

forEach, spliterator

Constructor Detail

IndexMaxPQ

public IndexMaxPQ(int maxN)

Initializes an empty indexed priority queue with indices between 0 and maxN - 1.

Parameters:

maxN - the keys on this priority queue are index from 0 to maxN - 1

Throws:

IllegalArgumentException - if maxN < 0

Method Detail

isEmpty

public boolean isEmpty()

Returns true if this priority queue is empty.

Returns:

true if this priority queue is empty; false otherwise

contains

public boolean contains(int i)

Is i an index on this priority queue?

Parameters:

i - an index

Returns:

true if i is an index on this priority queue; false otherwise

Throws:

IllegalArgumentException - unless 0 <= i < maxN

size

public int size()

Returns the number of keys on this priority queue.

Returns:

the number of keys on this priority queue

insert

public void insert(int i,
                   Key key)

Associate key with index i.

Parameters:

i - an index

key - the key to associate with index i

Throws:

IllegalArgumentException - unless 0 <= i < maxN

IllegalArgumentException - if there already is an item associated with index i

maxIndex

public int maxIndex()

Returns an index associated with a maximum key.

Returns:

an index associated with a maximum key

Throws:

NoSuchElementException - if this priority queue is empty

maxKey

public Key maxKey()

Returns a maximum key.

Returns:

a maximum key

Throws:

NoSuchElementException - if this priority queue is empty

delMax

public int delMax()

Removes a maximum key and returns its associated index.

Returns:

an index associated with a maximum key

Throws:

NoSuchElementException - if this priority queue is empty

keyOf

public Key keyOf(int i)

Returns the key associated with index i.

Parameters:

i - the index of the key to return

Returns:

the key associated with index i

Throws:

IllegalArgumentException - unless 0 <= i < maxN

NoSuchElementException - no key is associated with index i

changeKey

public void changeKey(int i,
                      Key key)

Change the key associated with index i to the specified value.

Parameters:

i - the index of the key to change

key - change the key associated with index i to this key

Throws:

IllegalArgumentException - unless 0 <= i < maxN

change

@Deprecated
public void change(int i,
                               Key key)

Deprecated. Replaced by changeKey(int, Key).

Change the key associated with index i to the specified value.

Parameters:

i - the index of the key to change

key - change the key associated with index i to this key

Throws:

IllegalArgumentException - unless 0 <= i < maxN

increaseKey

public void increaseKey(int i,
                        Key key)

Increase the key associated with index i to the specified value.

Parameters:

i - the index of the key to increase

key - increase the key associated with index i to this key

Throws:

IllegalArgumentException - unless 0 <= i < maxN

IllegalArgumentException - if key <= keyOf(i)

NoSuchElementException - no key is associated with index i

decreaseKey

public void decreaseKey(int i,
                        Key key)

Decrease the key associated with index i to the specified value.

Parameters:

i - the index of the key to decrease

key - decrease the key associated with index i to this key

Throws:

IllegalArgumentException - unless 0 <= i < maxN

IllegalArgumentException - if key >= keyOf(i)

NoSuchElementException - no key is associated with index i

delete

public void delete(int i)

Remove the key on the priority queue associated with index i.

Parameters:

i - the index of the key to remove

Throws:

IllegalArgumentException - unless 0 <= i < maxN

NoSuchElementException - no key is associated with index i

iterator

public Iterator<Integer> iterator()

Returns an iterator that iterates over the keys on the priority queue in descending order. The iterator doesn't implement remove() since it's optional.

Specified by:

iterator in interface Iterable<Integer>

Returns:

an iterator that iterates over the keys in descending order

main

public static void main(String[] args)

Unit tests the IndexMaxPQ data type.

Parameters:

args - the command-line arguments