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linkedhashset.go
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linkedhashset.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 linkedhashset is a set that preserves insertion-order.
//
// It is backed by a hash table to store values and doubly-linked list to store ordering.
//
// Note that insertion-order is not affected if an element is re-inserted into the set.
//
// Structure is not thread safe.
//
// References: http://en.wikipedia.org/wiki/Set_%28abstract_data_type%29
package linkedhashset
import (
"fmt"
"github.com/emirpasic/gods/lists/doublylinkedlist"
"github.com/emirpasic/gods/sets"
"strings"
)
// Assert Set implementation
var _ sets.Set = (*Set)(nil)
// Set holds elements in go's native map
type Set struct {
table map[interface{}]struct{}
ordering *doublylinkedlist.List
}
var itemExists = struct{}{}
// New instantiates a new empty set and adds the passed values, if any, to the set
func New(values ...interface{}) *Set {
set := &Set{
table: make(map[interface{}]struct{}),
ordering: doublylinkedlist.New(),
}
if len(values) > 0 {
set.Add(values...)
}
return set
}
// Add adds the items (one or more) to the set.
// Note that insertion-order is not affected if an element is re-inserted into the set.
func (set *Set) Add(items ...interface{}) {
for _, item := range items {
if _, contains := set.table[item]; !contains {
set.table[item] = itemExists
set.ordering.Append(item)
}
}
}
// Remove removes the items (one or more) from the set.
// Slow operation, worst-case O(n^2).
func (set *Set) Remove(items ...interface{}) {
for _, item := range items {
if _, contains := set.table[item]; contains {
delete(set.table, item)
index := set.ordering.IndexOf(item)
set.ordering.Remove(index)
}
}
}
// Contains check if items (one or more) are present in the set.
// All items have to be present in the set for the method to return true.
// Returns true if no arguments are passed at all, i.e. set is always superset of empty set.
func (set *Set) Contains(items ...interface{}) bool {
for _, item := range items {
if _, contains := set.table[item]; !contains {
return false
}
}
return true
}
// Empty returns true if set does not contain any elements.
func (set *Set) Empty() bool {
return set.Size() == 0
}
// Size returns number of elements within the set.
func (set *Set) Size() int {
return set.ordering.Size()
}
// Clear clears all values in the set.
func (set *Set) Clear() {
set.table = make(map[interface{}]struct{})
set.ordering.Clear()
}
// Values returns all items in the set.
func (set *Set) Values() []interface{} {
values := make([]interface{}, set.Size())
it := set.Iterator()
for it.Next() {
values[it.Index()] = it.Value()
}
return values
}
// String returns a string representation of container
func (set *Set) String() string {
str := "LinkedHashSet\n"
items := []string{}
it := set.Iterator()
for it.Next() {
items = append(items, fmt.Sprintf("%v", it.Value()))
}
str += strings.Join(items, ", ")
return str
}
// Intersection returns the intersection between two sets.
// The new set consists of all elements that are both in "set" and "another".
// Ref: https://en.wikipedia.org/wiki/Intersection_(set_theory)
func (set *Set) Intersection(another *Set) *Set {
result := New()
// Iterate over smaller set (optimization)
if set.Size() <= another.Size() {
for item := range set.table {
if _, contains := another.table[item]; contains {
result.Add(item)
}
}
} else {
for item := range another.table {
if _, contains := set.table[item]; contains {
result.Add(item)
}
}
}
return result
}
// Union returns the union of two sets.
// The new set consists of all elements that are in "set" or "another" (possibly both).
// Ref: https://en.wikipedia.org/wiki/Union_(set_theory)
func (set *Set) Union(another *Set) *Set {
result := New()
for item := range set.table {
result.Add(item)
}
for item := range another.table {
result.Add(item)
}
return result
}
// Difference returns the difference between two sets.
// The new set consists of all elements that are in "set" but not in "another".
// Ref: https://proofwiki.org/wiki/Definition:Set_Difference
func (set *Set) Difference(another *Set) *Set {
result := New()
for item := range set.table {
if _, contains := another.table[item]; !contains {
result.Add(item)
}
}
return result
}