NAME
BinaryHeap - Array-based binary heap supporting heapsort
SYNOPSIS
use BinaryHeap;
my BinaryHeap::MinHeap $heap;
$heap.push(42, 11);
say $heap.pop; # OUTPUT: «11»
say $heap.top; # OUTPUT: «42»
DESCRIPTION
role BinaryHeap[&infix:<precedes> = * cmp * == Less] {}
Role BinaryHeap stores values in an implicit binary tree that satisfies the heap property: the value of a node never precedes the value of its parent node.
Infix precedes defines a priority relation, such that the root of the tree, known as the top of the heap, has a priority higher than or equal to all other nodes of the tree. The default relation defines a min-heap, i.e. the top value compares Less than or Same as every other value on the heap.
Module BinaryHeap provides two classes that mix in the role:
class BinaryHeap::MaxHeap does BinaryHeap[* cmp * == More]
In a max-heap, a child node never compares More than its parent node.
class BinaryHeap::MinHeap does BinaryHeap[* cmp * == Less]
In a min-heap, a child node never compares Less than its parent node.
These classes are parameterizable with a custom three-way comparison operator. For example, this max-heap compares objects by their .key:
my BinaryHeap::MaxHeap[*.key cmp *.key] $heap;
An uninitialized BinaryHeap is a valid representation of an empty heap. This means that all documented methods can be called on a type object. Methods that may add values to the heap try to autovivify an uninitialized invocant, which means they can only be called on a container that stores or defaults to a class type. For example, given the uninitialized $heap declared above:
say $heap.values; # OUTPUT: «()»
say $heap.replace(42); # OUTPUT: «Nil»
say $heap.top; # OUTPUT: «42»
EXPORTS
infix eqv
Defined as:
multi sub infix:<eqv>(BinaryHeap \a, BinaryHeap \b --> Bool:D)
Returns True if and only if the two heaps are of the same type and contain equivalent values. Note that a concrete heap is of a different type than a role, so:
say BinaryHeap.new eqv BinaryHeap; # OUTPUT: «False»
say BinaryHeap::MaxHeap.new eqv BinaryHeap::MaxHeap; # OUTPUT: «True»
sub heapsort
Defined as:
multi sub heapsort(@array, :$reverse)
multi sub heapsort(&comparator, @array, :$reverse)
Sorts and returns the @array, using a custom three-way &comparator if provided. By default the array is sorted in ascending order, but it is sorted in descending order if :$reverse is true. Hence, the following statements both put the elements of the array in descending order:
heapsort @array, :reverse;
heapsort -(* cmp *), @array;
Note that heapsort is not a stable sort.
METHODS
method Bool
Defined as:
method Bool( --> Bool:D)
Returns True if the heap contains at least one node, and False if the heap is empty.
method clone
Defined as:
multi method clone(BinaryHeap:D: --> BinaryHeap:D)
Returns a clone of the invocant. The clone is based on a distinct array, so modifications to one heap will not affect the other heap.
method consume
Defined as:
method consume( --> Seq:D)
Returns a Seq that generates values by removing them from the top of the heap. If no values are inserted into the heap before the Seq is exhausted, the values will be in ascending order if called on a min-heap, in descending order if called on a max-heap.
method heapify
Defined as:
method heapify(@array --> BinaryHeap:D)
Constructs a new heap based on the provided array, whose elements are put in heap order. The @array should not be modified directly while the heap is in use.
method new
Defined as:
method new(+values --> BinaryHeap:D)
Constructs a new heap storing the provided values.
method pop
Defined as:
method pop()
Removes the value stored at the top of the heap and returns it, or returns a Failure if the heap is empty.
method push
Defined as:
method push(**@values --> BinaryHeap:D)
Inserts the provided values into the heap and returns the modified heap. Autovivifies the invocant if called on a container storing or defaulting to a class type object. For example:
my BinaryHeap::MaxHeap $heap;
$heap.push(42, 11);
say $heap.pop; # OUTPUT: «42»
say $heap.top; # OUTPUT: «11»
method push-pop
Defined as:
method push-pop(Mu \value)
Functionally equivalent, but more efficient than a push followed by a pop. Replaces the top of the heap if it precedes the provided value; otherwise just returns the provided value.
method replace
Defined as:
method replace(Mu \new)
Functionally equivalent, but more efficient than a pop followed by a push. Removes the top of the heap and returns it after inserting the new value.
method sort
Defined as:
method sort()
Returns an empty Array if called on an uninitialized heap. Otherwise sorts the underlying array in descending order if called on a min-heap, in ascending order if called on a max-heap. Replaces the underlying array with an empty copy and returns the sorted array.
method top
Defined as:
method top()
Returns the value stored at the top of the heap, or Nil if the heap is empty.
method values
Defined as:
method values( --> Seq:D)
Returns a Seq of the values encountered during a breadth-first traversal of the heap.
SEE ALSO
AUTHOR
Peter du Marchie van Voorthuysen
Source can be located at: https://github.com/dumarchie/raku-binaryheap
COPYRIGHT AND LICENSE
Copyright 2022 Peter du Marchie van Voorthuysen
This library is free software; you can redistribute it and/or modify it under the Artistic License 2.0.