Class: Heap

• Inheritance
• Description
• Class protocol
  • examples
  • instance creation
• Instance protocol
  • accessing
  • adding
  • comparing
  • enumerating
  • growing
  • private
  • private-heap
  • removing
  • testing
• Examples

Inheritance:

   Object
   |
   +--Collection
      |
      +--SequenceableCollection
         |
         +--Heap

Package:

stx:libbasic2

Category:

Collections-Sequenceable

Version:

rev: 1.2 date: 2009/11/27 21:18:23

user: cg

file: Heap.st directory: libbasic2

module: stx stc-classLibrary: libbasic2

Description:

Class Heap implements a special data structure commonly referred to as 'heap'.
Heaps are more efficient than SortedCollections if:
    a) Elements are only removed at the beginning
    b) Elements are added with arbitrary sort order.

The sort time for a heap is O(n log n) in all cases.
Instance variables:
    array           <Array>         the data repository
    tally           <Integer>       the number of elements in the heap
    sortBlock       <Block|nil>     a two-argument block defining the sort order,
                                    or nil in which case the default sort order is
                                        [:element1 :element2| element1 <= element2]

Class protocol:

 documentation

Class Heap implements a special data structure commonly referred to as 'heap'.
Heaps are more efficient than SortedCollections if:
a) Elements are only removed at the beginning
b) Elements are added with arbitrary sort order.

The sort time for a heap is O(n log n) in all cases.
Instance variables:
array <Array> the data repository
tally <Integer> the number of elements in the heap
sortBlock <Block|nil> a two-argument block defining the sort order,
or nil in which case the default sort order is
[:element1 :element2| element1 <= element2]

 examples

Create a sorted collection of numbers, remove the elements
sequentially and add new objects randomly.
Note: This is the kind of benchmark a heap is designed for.
[exBegin]
| n rnd array time sorted |
n := 50000.
rnd := Random new.
array := (1 to: n) collect:[:i| rnd next].

time := Time millisecondsToRun:[
sorted := Heap withAll: array.
1 to: n do:[:i|
sorted removeFirst.
sorted add: rnd next].
].
Transcript showCR:'Time for Heap: ', time printString,' msecs'.

time := Time millisecondsToRun:[
sorted := SortedCollection withAll: array.
1 to: n do:[:i|
sorted removeFirst.
sorted add: rnd next].
].
Transcript showCR:'Time for SortedCollection: ', time printString,' msecs'.
[exEnd]

Sort a random collection of Floats and compare the results with
SortedCollection (using the quick-sort algorithm) and
[exBegin]
| n rnd array out time sorted |
n := 40000.
rnd := Random new.
array := (1 to: n) collect:[:i| rnd next].

out := Array new: n.
time := Time millisecondsToRun:[
sorted := Heap withAll: array.
1 to: n do:[:i| sorted removeFirst].
].
Transcript showCR:'Time for heap-sort: ', time printString,' msecs'.

time := Time millisecondsToRun:[
sorted := SortedCollection withAll: array.
].
Transcript showCR:'Time for quick-sort: ', time printString,' msecs'.
[exEnd]

 new

 new: n

 sortBlock: aBlock

Create a new heap sorted by the given block

 withAll: aCollection

Create a new heap with all the elements from aCollection

 withAll: aCollection sortBlock: sortBlock

Create a new heap with all the elements from aCollection

Instance protocol:

 at: index

Return the element at the given position within the receiver

 at: index put: newObject

Heaps are accessed with #add: not #at:put:

 first

Return the first element in the receiver

 firstOrNil

 reSort

Resort the entire heap

 size

Answer how many elements the receiver contains.

 sortBlock

 sortBlock: aBlock

 add: anObject

Include newObject as one of the receiver's elements. Answer newObject.

 = anObject

 do: aBlock

Evaluate aBlock with each of the receiver's elements as the argument.

 grow

Become larger.

 growSize

Return the size by which the receiver should grow if there are no empty slots left.

 growTo: newSize

Grow to the requested size.

 trim

Remove any empty slots in the receiver.

 array

 privateRemoveAt: index

Remove the element at the given index and make sure the sorting order is okay

 setCollection: aCollection

 setCollection: aCollection tally: newTally

 species

 downHeap: anIndex

Check the heap downwards for correctness starting at anIndex.
Everything above (i.e. left of) anIndex is ok.

 downHeapSingle: anIndex

This version is optimized for the case when only one element in the receiver can be at a wrong position. It avoids one comparison at each node when travelling down the heap and checks the heap upwards after the element is at a bottom position. Since the probability for being at the bottom of the heap is much larger than for being somewhere in the middle this version should be faster.

 upHeap: anIndex

Check the heap upwards for correctness starting at anIndex.
Everything below anIndex is ok.

 remove: oldObject ifAbsent: aBlock

Remove oldObject as one of the receiver's elements. If several of the
elements are equal to oldObject, only one is removed. If no element is
equal to oldObject, answer the result of evaluating anExceptionBlock.
Otherwise, answer the argument, oldObject.

 removeAt: index

Remove the element at given position

 removeFirst

Remove the first element from the receiver

 isEmpty

Answer whether the receiver contains any elements.

 isHeap

 sorts: element1 before: element2

Return true if element1 should be sorted before element2.
This method defines the sort order in the receiver

Examples:

    | n rnd array time sorted |
    n := 50000. 
    rnd := Random new.
    array := (1 to: n) collect:[:i| rnd next].

    time := Time millisecondsToRun:[
            sorted := Heap withAll: array.
            1 to: n do:[:i| 
                    sorted removeFirst.
                    sorted add: rnd next].
    ].
    Transcript showCR:'Time for Heap: ', time printString,' msecs'.

    time := Time millisecondsToRun:[
            sorted := SortedCollection withAll: array.
            1 to: n do:[:i| 
                    sorted removeFirst.
                    sorted add: rnd next].
    ].
    Transcript showCR:'Time for SortedCollection: ', time printString,' msecs'.

    | n rnd array out time sorted |
    n := 40000. 
    rnd := Random new.
    array := (1 to: n) collect:[:i| rnd next].

    out := Array new: n. 
    time := Time millisecondsToRun:[
            sorted := Heap withAll: array.
            1 to: n do:[:i| sorted removeFirst].
    ].
    Transcript showCR:'Time for heap-sort: ', time printString,' msecs'.

    time := Time millisecondsToRun:[
            sorted := SortedCollection withAll: array.
    ].
    Transcript showCR:'Time for quick-sort: ', time printString,' msecs'.