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245 lines
8.1 KiB
Go
245 lines
8.1 KiB
Go
/*
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Copyright (c) 2015, Emir Pasic
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All rights reserved.
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions are met:
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* Redistributions of source code must retain the above copyright notice, this
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list of conditions and the following disclaimer.
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* Redistributions in binary form must reproduce the above copyright notice,
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this list of conditions and the following disclaimer in the documentation
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and/or other materials provided with the distribution.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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// Package binaryheap implements a binary heap backed by array list.
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//
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// Comparator defines this heap as either min or max heap.
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//
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// Structure is not thread safe.
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//
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// References: http://en.wikipedia.org/wiki/Binary_heap
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package binaryheap
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import (
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"fmt"
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"github.com/emirpasic/gods/containers"
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"github.com/emirpasic/gods/lists/arraylist"
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"github.com/emirpasic/gods/trees"
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"github.com/emirpasic/gods/utils"
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"strings"
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)
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func assertInterfaceImplementation() {
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var _ trees.Tree = (*Heap)(nil)
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var _ containers.ReverseIteratorWithIndex = (*Iterator)(nil)
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}
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// Heap holds elements in an array-list
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type Heap struct {
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list *arraylist.List
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Comparator utils.Comparator
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}
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// NewWith instantiates a new empty heap tree with the custom comparator.
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func NewWith(comparator utils.Comparator) *Heap {
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return &Heap{list: arraylist.New(), Comparator: comparator}
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}
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// NewWithIntComparator instantiates a new empty heap with the IntComparator, i.e. elements are of type int.
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func NewWithIntComparator() *Heap {
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return &Heap{list: arraylist.New(), Comparator: utils.IntComparator}
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}
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// NewWithStringComparator instantiates a new empty heap with the StringComparator, i.e. elements are of type string.
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func NewWithStringComparator() *Heap {
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return &Heap{list: arraylist.New(), Comparator: utils.StringComparator}
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}
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// Push adds a value onto the heap and bubbles it up accordingly.
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func (heap *Heap) Push(value interface{}) {
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heap.list.Add(value)
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heap.bubbleUp()
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}
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// Pop removes top element on heap and returns it, or nil if heap is empty.
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// Second return parameter is true, unless the heap was empty and there was nothing to pop.
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func (heap *Heap) Pop() (value interface{}, ok bool) {
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value, ok = heap.list.Get(0)
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if !ok {
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return
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}
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lastIndex := heap.list.Size() - 1
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heap.list.Swap(0, lastIndex)
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heap.list.Remove(lastIndex)
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heap.bubbleDown()
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return
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}
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// Peek returns top element on the heap without removing it, or nil if heap is empty.
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// Second return parameter is true, unless the heap was empty and there was nothing to peek.
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func (heap *Heap) Peek() (value interface{}, ok bool) {
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return heap.list.Get(0)
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}
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// Empty returns true if heap does not contain any elements.
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func (heap *Heap) Empty() bool {
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return heap.list.Empty()
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}
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// Size returns number of elements within the heap.
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func (heap *Heap) Size() int {
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return heap.list.Size()
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}
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// Clear removes all elements from the heap.
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func (heap *Heap) Clear() {
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heap.list.Clear()
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}
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// Values returns all elements in the heap.
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func (heap *Heap) Values() []interface{} {
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return heap.list.Values()
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}
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// Iterator returns a stateful iterator whose values can be fetched by an index.
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type Iterator struct {
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heap *Heap
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index int
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}
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// Iterator returns a stateful iterator whose values can be fetched by an index.
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func (heap *Heap) Iterator() Iterator {
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return Iterator{heap: heap, index: -1}
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}
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// Next moves the iterator to the next element and returns true if there was a next element in the container.
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// If Next() returns true, then next element's index and value can be retrieved by Index() and Value().
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// If Next() was called for the first time, then it will point the iterator to the first element if it exists.
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// Modifies the state of the iterator.
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func (iterator *Iterator) Next() bool {
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if iterator.index < iterator.heap.Size() {
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iterator.index++
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}
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return iterator.heap.withinRange(iterator.index)
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}
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// Prev moves the iterator to the previous element and returns true if there was a previous element in the container.
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// If Prev() returns true, then previous element's index and value can be retrieved by Index() and Value().
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// Modifies the state of the iterator.
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func (iterator *Iterator) Prev() bool {
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if iterator.index >= 0 {
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iterator.index--
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}
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return iterator.heap.withinRange(iterator.index)
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}
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// Value returns the current element's value.
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// Does not modify the state of the iterator.
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func (iterator *Iterator) Value() interface{} {
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value, _ := iterator.heap.list.Get(iterator.index)
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return value
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}
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// Index returns the current element's index.
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// Does not modify the state of the iterator.
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func (iterator *Iterator) Index() int {
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return iterator.index
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}
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// Begin resets the iterator to its initial state (one-before-first)
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// Call Next() to fetch the first element if any.
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func (iterator *Iterator) Begin() {
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iterator.index = -1
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}
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// End moves the iterator past the last element (one-past-the-end).
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// Call Prev() to fetch the last element if any.
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func (iterator *Iterator) End() {
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iterator.index = iterator.heap.Size()
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}
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// First moves the iterator to the first element and returns true if there was a first element in the container.
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// If First() returns true, then first element's index and value can be retrieved by Index() and Value().
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// Modifies the state of the iterator.
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func (iterator *Iterator) First() bool {
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iterator.Begin()
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return iterator.Next()
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}
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// Last moves the iterator to the last element and returns true if there was a last element in the container.
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// If Last() returns true, then last element's index and value can be retrieved by Index() and Value().
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// Modifies the state of the iterator.
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func (iterator *Iterator) Last() bool {
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iterator.End()
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return iterator.Prev()
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}
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// String returns a string representation of container
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func (heap *Heap) String() string {
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str := "BinaryHeap\n"
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values := []string{}
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for _, value := range heap.list.Values() {
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values = append(values, fmt.Sprintf("%v", value))
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}
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str += strings.Join(values, ", ")
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return str
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}
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// Performs the "bubble down" operation. This is to place the element that is at the
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// root of the heap in its correct place so that the heap maintains the min/max-heap order property.
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func (heap *Heap) bubbleDown() {
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index := 0
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size := heap.list.Size()
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for leftIndex := index<<1 + 1; leftIndex < size; leftIndex = index<<1 + 1 {
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rightIndex := index<<1 + 2
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smallerIndex := leftIndex
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leftValue, _ := heap.list.Get(leftIndex)
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rightValue, _ := heap.list.Get(rightIndex)
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if rightIndex < size && heap.Comparator(leftValue, rightValue) > 0 {
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smallerIndex = rightIndex
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}
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indexValue, _ := heap.list.Get(index)
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smallerValue, _ := heap.list.Get(smallerIndex)
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if heap.Comparator(indexValue, smallerValue) > 0 {
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heap.list.Swap(index, smallerIndex)
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} else {
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break
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}
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index = smallerIndex
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}
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}
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// Performs the "bubble up" operation. This is to place a newly inserted
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// element (i.e. last element in the list) in its correct place so that
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// the heap maintains the min/max-heap order property.
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func (heap *Heap) bubbleUp() {
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index := heap.list.Size() - 1
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for parentIndex := (index - 1) >> 1; index > 0; parentIndex = (index - 1) >> 1 {
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indexValue, _ := heap.list.Get(index)
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parentValue, _ := heap.list.Get(parentIndex)
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if heap.Comparator(parentValue, indexValue) <= 0 {
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break
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}
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heap.list.Swap(index, parentIndex)
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index = parentIndex
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}
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}
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// Check that the index is within bounds of the list
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func (heap *Heap) withinRange(index int) bool {
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return index >= 0 && index < heap.list.Size()
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}
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