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arraylist.go
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arraylist.go
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// 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 arraylist implements the array list.
//
// Structure is not thread safe.
//
// Reference: https://en.wikipedia.org/wiki/List_%28abstract_data_type%29
package arraylist
import (
"fmt"
"github.com/emirpasic/gods/lists"
"github.com/emirpasic/gods/utils"
"strings"
)
func assertListImplementation() {
var _ lists.List = (*List)(nil)
}
// List holds the elements in a slice
type List struct {
elements []interface{}
size int
}
const (
growthFactor = float32(2.0) // growth by 100%
shrinkFactor = float32(0.25) // shrink when size is 25% of capacity (0 means never shrink)
)
// New instantiates a new empty list
func New() *List {
return &List{}
}
// Add appends a value at the end of the list
func (list *List) Add(values ...interface{}) {
list.growBy(len(values))
for _, value := range values {
list.elements[list.size] = value
list.size++
}
}
// Get returns the element at index.
// Second return parameter is true if index is within bounds of the array and array is not empty, otherwise false.
func (list *List) Get(index int) (interface{}, bool) {
if !list.withinRange(index) {
return nil, false
}
return list.elements[index], true
}
// Remove removes one or more elements from the list with the supplied indices.
func (list *List) Remove(index int) {
if !list.withinRange(index) {
return
}
list.elements[index] = nil // cleanup reference
copy(list.elements[index:], list.elements[index+1:list.size]) // shift to the left by one (slow operation, need ways to optimize this)
list.size--
list.shrink()
}
// Contains checks if elements (one or more) are present in the set.
// All elements have to be present in the set for the method to return true.
// Performance time complexity of n^2.
// Returns true if no arguments are passed at all, i.e. set is always super-set of empty set.
func (list *List) Contains(values ...interface{}) bool {
for _, searchValue := range values {
found := false
for _, element := range list.elements {
if element == searchValue {
found = true
break
}
}
if !found {
return false
}
}
return true
}
// Values returns all elements in the list.
func (list *List) Values() []interface{} {
newElements := make([]interface{}, list.size, list.size)
copy(newElements, list.elements[:list.size])
return newElements
}
// Empty returns true if list does not contain any elements.
func (list *List) Empty() bool {
return list.size == 0
}
// Size returns number of elements within the list.
func (list *List) Size() int {
return list.size
}
// Clear removes all elements from the list.
func (list *List) Clear() {
list.size = 0
list.elements = []interface{}{}
}
// Sort sorts values (in-place) using.
func (list *List) Sort(comparator utils.Comparator) {
if len(list.elements) < 2 {
return
}
utils.Sort(list.elements[:list.size], comparator)
}
// Swap swaps the two values at the specified positions.
func (list *List) Swap(i, j int) {
if list.withinRange(i) && list.withinRange(j) {
list.elements[i], list.elements[j] = list.elements[j], list.elements[i]
}
}
// Insert inserts values at specified index position shifting the value at that position (if any) and any subsequent elements to the right.
// Does not do anything if position is negative or bigger than list's size
// Note: position equal to list's size is valid, i.e. append.
func (list *List) Insert(index int, values ...interface{}) {
if !list.withinRange(index) {
// Append
if index == list.size {
list.Add(values...)
}
return
}
l := len(values)
list.growBy(l)
list.size += l
// Shift old to right
for i := list.size - 1; i >= index+l; i-- {
list.elements[i] = list.elements[i-l]
}
// Insert new
for i, value := range values {
list.elements[index+i] = value
}
}
// String returns a string representation of container
func (list *List) String() string {
str := "ArrayList\n"
values := []string{}
for _, value := range list.elements[:list.size] {
values = append(values, fmt.Sprintf("%v", value))
}
str += strings.Join(values, ", ")
return str
}
// Check that the index is within bounds of the list
func (list *List) withinRange(index int) bool {
return index >= 0 && index < list.size
}
func (list *List) resize(cap int) {
newElements := make([]interface{}, cap, cap)
copy(newElements, list.elements)
list.elements = newElements
}
// Expand the array if necessary, i.e. capacity will be reached if we add n elements
func (list *List) growBy(n int) {
// When capacity is reached, grow by a factor of growthFactor and add number of elements
currentCapacity := cap(list.elements)
if list.size+n >= currentCapacity {
newCapacity := int(growthFactor * float32(currentCapacity+n))
list.resize(newCapacity)
}
}
// Shrink the array if necessary, i.e. when size is shrinkFactor percent of current capacity
func (list *List) shrink() {
if shrinkFactor == 0.0 {
return
}
// Shrink when size is at shrinkFactor * capacity
currentCapacity := cap(list.elements)
if list.size <= int(float32(currentCapacity)*shrinkFactor) {
list.resize(list.size)
}
}