Arafatk/DataViz

// Package binaryheap implements a binary heap backed by array list.
//
// Comparator defines this heap as either min or max heap.
//
// Structure is not thread safe.
//
// References: http://en.wikipedia.org/wiki/Binary_heap
package binaryheap

import (
    "fmt"
    "strconv"
    "strings"

    "github.com/Arafatk/Dataviz/lists/arraylist"
    "github.com/Arafatk/Dataviz/trees"
    "github.com/Arafatk/Dataviz/utils"
)

func assertTreeImplementation() {
    var _ trees.Tree = (*Heap)(nil)
}

// Heap holds elements in an array-list
type Heap struct {
    list       *arraylist.List
    Comparator utils.Comparator
}

// NewWith instantiates a new empty heap tree with the custom comparator.
func NewWith(comparator utils.Comparator) *Heap {
    return &Heap{list: arraylist.New(), Comparator: comparator}
}

// NewWithIntComparator instantiates a new empty heap with the IntComparator, i.e. elements are of type int.
func NewWithIntComparator() *Heap {
    return &Heap{list: arraylist.New(), Comparator: utils.IntComparator}
}

// NewWithStringComparator instantiates a new empty heap with the StringComparator, i.e. elements are of type string.
func NewWithStringComparator() *Heap {
    return &Heap{list: arraylist.New(), Comparator: utils.StringComparator}
}

// Push adds a value onto the heap and bubbles it up accordingly.
func (heap *Heap) Push(values ...interface{}) {
    if len(values) == 1 {
        heap.list.Add(values[0])
        heap.bubbleUp()
    } else {
        // Reference: https://en.wikipedia.org/wiki/Binary_heap#Building_a_heap
        for _, value := range values {
            heap.list.Add(value)
        }
        size := heap.list.Size()/2 + 1
        for i := size; i >= 0; i-- {
            heap.bubbleDownIndex(i)
        }
    }
}

// Pop removes top element on heap and returns it, or nil if heap is empty.
// Second return parameter is true, unless the heap was empty and there was nothing to pop.
func (heap *Heap) Pop() (value interface{}, ok bool) {
    value, ok = heap.list.Get(0)
    if !ok {
        return
    }
    lastIndex := heap.list.Size() - 1
    heap.list.Swap(0, lastIndex)
    heap.list.Remove(lastIndex)
    heap.bubbleDown()
    return
}

// Peek returns top element on the heap without removing it, or nil if heap is empty.
// Second return parameter is true, unless the heap was empty and there was nothing to peek.
func (heap *Heap) Peek() (value interface{}, ok bool) {
    return heap.list.Get(0)
}

// Empty returns true if heap does not contain any elements.
func (heap *Heap) Empty() bool {
    return heap.list.Empty()
}

// Size returns number of elements within the heap.
func (heap *Heap) Size() int {
    return heap.list.Size()
}

// Clear removes all elements from the heap.
func (heap *Heap) Clear() {
    heap.list.Clear()
}

// Values returns all elements in the heap.
func (heap *Heap) Values() []interface{} {
    return heap.list.Values()
}

// String returns a string representation of container
func (heap *Heap) String() string {
    str := "BinaryHeap\n"
    values := []string{}
    for _, value := range heap.list.Values() {
        values = append(values, fmt.Sprintf("%v", value))
    }
    str += strings.Join(values, ", ")
    return str
}

// Performs the "bubble down" operation. This is to place the element that is at the root
// of the heap in its correct place so that the heap maintains the min/max-heap order property.
func (heap *Heap) bubbleDown() {
    heap.bubbleDownIndex(0)
}

// Performs the "bubble down" operation. This is to place the element that is at the index
// of the heap in its correct place so that the heap maintains the min/max-heap order property.
func (heap *Heap) bubbleDownIndex(index int) {
    size := heap.list.Size()
    for leftIndex := index<<1 + 1; leftIndex < size; leftIndex = index<<1 + 1 {
        rightIndex := index<<1 + 2
        smallerIndex := leftIndex
        leftValue, _ := heap.list.Get(leftIndex)
        rightValue, _ := heap.list.Get(rightIndex)
        if rightIndex < size && heap.Comparator(leftValue, rightValue) > 0 {
            smallerIndex = rightIndex
        }
        indexValue, _ := heap.list.Get(index)
        smallerValue, _ := heap.list.Get(smallerIndex)
        if heap.Comparator(indexValue, smallerValue) > 0 {
            heap.list.Swap(index, smallerIndex)
        } else {
            break
        }
        index = smallerIndex
    }
}

// Visualizer makes a visual image demonstrating the heap data structure
// using dot language and Graphviz. It first producs a dot string corresponding
// to the heap and then runs graphviz to output the resulting image to a file.
func (heap *Heap) Visualizer(fileName string) bool {
    size := heap.Size()
    indexValueMap := make(map[int]interface{})
    dotString := "digraph graphname{bgcolor=white;"
    stringValues := []string{}
    for i := 0; i < (2 * size); i++ {
        value, exists := heap.list.Get(i)
        if exists {
            indexValueMap[i] = value // Anybody who exists is connected to parent
            if i != 0 {
                dotString += (strconv.Itoa((i-1)/2) + " -> " + strconv.Itoa((i)) + ";")
                stringValues = append(stringValues, fmt.Sprintf("%v", value))
                dotString += (strconv.Itoa(i) + "[color=steelblue1, style=filled, fillcolor = steelblue1, fontcolor=white,label=" + stringValues[len(stringValues)-1] + "];")

            } else {
                stringValues = append(stringValues, fmt.Sprintf("%v", value))
                dotString += (strconv.Itoa(i) + "[color=steelblue1, style=filled, fillcolor = steelblue1, fontcolor=white,label=" + stringValues[len(stringValues)-1] + "];")

            }
        }
    }
    dotString += "}"

    return utils.WriteDotStringToPng(fileName, dotString)
}

// Performs the "bubble up" operation. This is to place a newly inserted
// element (i.e. last element in the list) in its correct place so that
// the heap maintains the min/max-heap order property.
func (heap *Heap) bubbleUp() {
    index := heap.list.Size() - 1
    for parentIndex := (index - 1) >> 1; index > 0; parentIndex = (index - 1) >> 1 {
        indexValue, _ := heap.list.Get(index)
        parentValue, _ := heap.list.Get(parentIndex)
        if heap.Comparator(parentValue, indexValue) <= 0 {
            break
        }
        heap.list.Swap(index, parentIndex)
        index = parentIndex
    }
}

// Check that the index is within bounds of the list
func (heap *Heap) withinRange(index int) bool {
    return index >= 0 && index < heap.list.Size()
}