Package edu.princeton.cs.algs4

Class IndexMinPQ<Key extends Comparable<Key>>

  • Type Parameters:
    Key - the generic type of key on this priority queue
    All Implemented Interfaces:
    Iterable<Integer>
    public class IndexMinPQ<Key extends Comparable<Key>>
extends Object
implements Iterable<Integer>
    The IndexMinPQ class represents an indexed priority queue of generic keys. It supports the usual insert and delete-the-minimum operations, along with delete and change-the-key methods. In order to let the client refer to keys 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 the minimum 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-minimum, 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 Description
      IndexMinPQ​(int maxN)
      Initializes an empty indexed priority queue with indices between 0 and maxN - 1.

    • Constructor Detail

      • IndexMinPQ

        public IndexMinPQ​(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 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)
        Associates 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

      • minIndex

        public int minIndex()
        Returns an index associated with a minimum key.
        Returns:
        an index associated with a minimum key
        Throws:
        NoSuchElementException - if this priority queue is empty

      • minKey

        public Key minKey()
        Returns a minimum key.
        Returns:
        a minimum key
        Throws:
        NoSuchElementException - if this priority queue is empty

      • delMin

        public int delMin()
        Removes a minimum key and returns its associated index.
        Returns:
        an index associated with a minimum 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
        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

      • 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

      • delete

        public void delete​(int i)
        Remove the key 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 ascending order. The iterator doesn't implement remove() since it's optional.
        Specified by:
        iterator in interface Iterable<Key extends Comparable<Key>>
        Returns:
        an iterator that iterates over the keys in ascending order

      • main

        public static void main​(String[] args)
        Unit tests the IndexMinPQ data type.
        Parameters:
        args - the command-line arguments