You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
 
 
 
 
 
 
gitea/vendor/github.com/emirpasic/gods/trees/binaryheap/binaryheap.go

163 lines
4.9 KiB

// Copyright (c) 2015, Emir Pasic. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// 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"
"github.com/emirpasic/gods/lists/arraylist"
"github.com/emirpasic/gods/trees"
"github.com/emirpasic/gods/utils"
"strings"
)
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
}
}
// 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()
}