Merge pull request emirpasic#148 from AryanAhadinia/issue_146

Add Queue

README.md

@@ -18,6 +18,9 @@ Implementation of various data structures and algorithms in Go.
     - [ArrayList](#arraylist)
     - [SinglyLinkedList](#singlylinkedlist)
     - [DoublyLinkedList](#doublylinkedlist)
+  - [Queues](#queues)
+    - [LinkedListQueue](#linkedlistqueue)
+    - [ArrayQueue](#arrayqueue)
   - [Sets](#sets)
     - [HashSet](#hashset)
     - [TreeSet](#treeset)
@@ -76,6 +79,9 @@ Containers are either ordered or unordered. All ordered containers provide [stat
 |   | [ArrayList](#arraylist) | yes | yes* | yes | index |
 |   | [SinglyLinkedList](#singlylinkedlist) | yes | yes | yes | index |
 |   | [DoublyLinkedList](#doublylinkedlist) | yes | yes* | yes | index |
+| [Queues](#queues) |
+|   | [LinkedListQueues](#linkedlistqueues) | yes | yes | no | index |
+|   | [ArrayQueues](#arrayqueues) | yes | yes* | no | index |
 | [Sets](#sets) |
 |   | [HashSet](#hashset) | no | no | no | index |
 |   | [TreeSet](#treeset) | yes | yes* | yes | index |
@@ -416,6 +422,80 @@ func main() {
 }
 ```
 
+### Queues
+
+A queue that represents a first-in-first-out (FIFO) data structure. The usual enqueue and dequeue operations are provided, as well as a method to peek at the first item in the queue.
+
+Implements [Container](#containers) interface.
+
+```go
+type Queue interface {
+	Enqueue(value interface{})
+	Dequeue() (value interface{}, ok bool)
+	Peek() (value interface{}, ok bool)
+
+	containers.Container
+	// Empty() bool
+	// Size() int
+	// Clear()
+	// Values() []interface{}
+}
+```
+
+#### LinkedListQueue
+
+A [queue](#queues) based on a [linked list](#singlylinkedlist).
+
+Implements [Queue](#queues), [IteratorWithIndex](#iteratorwithindex), [JSONSerializer](#jsonserializer) and [JSONDeserializer](#jsondeserializer) interfaces.
+
+```go
+package main
+
+import ll1 "github.com/emirpasic/gods/stacks/linkedlistqueue"
+
+func main() {
+	queue := llq.New()  	// empty
+	queue.Enqueue(1)    	// 1
+	queue.Enqueue(2)       	// 1, 2
+	queue.Values()      	// 1, 2
+	_, _ = queue.Peek() 	// 1, true
+	_, _ = queue.Dequeue()  // 1, true
+	_, _ = queue.Dequeue()  // 2, true
+	_, _ = queue.Dequeue()  // nil, false
+	queue.Enqueue(1)       	// 1
+	queue.Clear()      		// empty
+	queue.Empty()      		// true
+	queue.Size()       		// 0
+}
+```
+
+#### ArrayQueue
+
+A [queue](#queues) based on a [array list](#arraylist).
+
+Implements [Queue](#queues), [IteratorWithIndex](#iteratorwithindex), [JSONSerializer](#jsonserializer) and [JSONDeserializer](#jsondeserializer) interfaces.
+
+```go
+package main
+
+import ll1 "github.com/emirpasic/gods/stacks/linkedlistqueue"
+
+func main() {
+	queue := llq.New()  	// empty
+	queue.Enqueue(1)    	// 1
+	queue.Enqueue(2)       	// 1, 2
+	queue.Values()      	// 1, 2
+	_, _ = queue.Peek() 	// 1, true
+	_, _ = queue.Dequeue()  // 1, true
+	_, _ = queue.Dequeue()  // 2, true
+	_, _ = queue.Dequeue()  // nil, false
+	queue.Enqueue(1)       	// 1
+	queue.Clear()      		// empty
+	queue.Empty()      		// true
+	queue.Size()       		// 0
+}
+```
+
 ### Maps
 
 A Map is a data structure that maps keys to values. A map cannot contain duplicate keys and each key can map to at most one value.

queues/arrayqueue/arrayqueue.go

@@ -0,0 +1,87 @@
+// Copyright (c) 2021, Aryan Ahadinia. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package arrayqueue implements a queue backed by a array-list.
+//
+// Structure is not thread safe.
+//
+// Reference: https://en.wikipedia.org/wiki/Queue_(abstract_data_type)
+package arrayqueue
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/emirpasic/gods/lists/arraylist"
+	"github.com/emirpasic/gods/queues"
+)
+
+func assertQueueImplementation() {
+	var _ queues.Queue = (*Queue)(nil)
+}
+
+// Queue holds elements in an array-list
+type Queue struct {
+	list *arraylist.List
+}
+
+// New instantiates a new empty queue
+func New() *Queue {
+	return &Queue{list: arraylist.New()}
+}
+
+// Enqueue adds a value to the end of the queue
+func (queue *Queue) Enqueue(value interface{}) {
+	queue.list.Add(value)
+}
+
+// Dequeue removes first element of the queue and returns it, or nil if queue is empty.
+// Second return parameter is true, unless the queue was empty and there was nothing to dequeue.
+func (queue *Queue) Dequeue() (value interface{}, ok bool) {
+	value, ok = queue.list.Get(0)
+	queue.list.Remove(0)
+	return
+}
+
+// Peek returns first element of the queue without removing it, or nil if queue is empty.
+// Second return parameter is true, unless the queue was empty and there was nothing to peek.
+func (queue *Queue) Peek() (value interface{}, ok bool) {
+	return queue.list.Get(0)
+}
+
+// Empty returns true if queue does not contain any elements.
+func (queue *Queue) Empty() bool {
+	return queue.list.Empty()
+}
+
+// Size returns number of elements within the queue.
+func (queue *Queue) Size() int {
+	return queue.list.Size()
+}
+
+// Clear removes all elements from the queue.
+func (queue *Queue) Clear() {
+	queue.list.Clear()
+}
+
+// Values returns all elements in the queue (FIFO order).
+func (queue *Queue) Values() []interface{} {
+	return queue.list.Values()
+}
+
+// String returns a string representation of container
+func (queue *Queue) String() string {
+	str := "ArrayQueue\n"
+	values := []string{}
+	for _, value := range queue.list.Values() {
+		values = append(values, fmt.Sprintf("%v", value))
+	}
+	str += strings.Join(values, ", ")
+	return str
+}
+
+// Check that the index is within bounds of the list
+func (queue *Queue) withinRange(index int) bool {
+	return index >= 0 && index < queue.list.Size()
+}