- add reversible iterators to array stack

README.md

@@ -56,16 +56,16 @@ Containers are either ordered or unordered. All ordered containers provide [stat
 | Container | Ordered | [Iterator](#iterator) | [Enumerable](#enumerable) | Ordered by |
 | :--- | :---: | :---: | :---: | :---: |
 | [ArrayList](#arraylist) | yes | yes* | yes | index |
-| [SinglyLinkedList](#singlylinkedlist) | yes | yes* | yes | index |
+| [SinglyLinkedList](#singlylinkedlist) | yes | yes | yes | index |
 | [DoublyLinkedList](#doublylinkedlist) | yes | yes* | yes | index |
 | [HashSet](#hashset) | no | no | no | index |
-| [TreeSet](#treeset) | yes | yes | yes | index |
+| [TreeSet](#treeset) | yes | yes* | yes | index |
 | [LinkedListStack](#linkedliststack) | yes | yes | no | index |
-| [ArrayStack](#arraystack) | yes | yes | no | index |
+| [ArrayStack](#arraystack) | yes | yes* | no | index |
 | [HashMap](#hashmap) | no | no | no | key |
-| [TreeMap](#treemap) | yes | yes | yes | key |
-| [RedBlackTree](#redblacktree) | yes | yes | no | key |
-| [BinaryHeap](#binaryheap) | yes | yes | no | index |
+| [TreeMap](#treemap) | yes | yes* | yes | key |
+| [RedBlackTree](#redblacktree) | yes | yes* | no | key |
+| [BinaryHeap](#binaryheap) | yes | yes* | no | index |
 |  |  | <sub><sup>*reversible</sup></sub> |  |  |
 
 ### Lists

maps/treemap/treemap_test.go

@@ -318,7 +318,9 @@ func TestMapIterator(t *testing.T) {
 	m.Put("b", 2)
 
 	it := m.Iterator()
+	count := 0
 	for it.Next() {
+		count++
 		key := it.Key()
 		value := it.Value()
 		switch key {
@@ -337,6 +339,12 @@ func TestMapIterator(t *testing.T) {
 		default:
 			t.Errorf("Too many")
 		}
+		if actualValue, expectedValue := value, count; actualValue != expectedValue {
+			t.Errorf("Got %v expected %v", actualValue, expectedValue)
+		}
+	}
+	if actualValue, expectedValue := count, 3; actualValue != expectedValue {
+		t.Errorf("Got %v expected %v", actualValue, expectedValue)
 	}
 
 	m.Clear()

sets/treeset/treeset_test.go

@@ -197,7 +197,9 @@ func TestSetIterator(t *testing.T) {
 	set.Add("c", "a", "b")
 
 	it := set.Iterator()
+	count := 0
 	for it.Next() {
+		count++
 		index := it.Index()
 		value := it.Value()
 		switch index {
@@ -216,6 +218,12 @@ func TestSetIterator(t *testing.T) {
 		default:
 			t.Errorf("Too many")
 		}
+		if actualValue, expectedValue := index, count-1; actualValue != expectedValue {
+			t.Errorf("Got %v expected %v", actualValue, expectedValue)
+		}
+	}
+	if actualValue, expectedValue := count, 3; actualValue != expectedValue {
+		t.Errorf("Got %v expected %v", actualValue, expectedValue)
 	}
 
 	set.Clear()

stacks/arraystack/arraystack.go

@@ -41,7 +41,7 @@ import (
 
 func assertInterfaceImplementation() {
 	var _ stacks.Stack = (*Stack)(nil)
-	var _ containers.IteratorWithIndex = (*Iterator)(nil)
+	var _ containers.ReverseIteratorWithIndex = (*Iterator)(nil)
 }
 
 // Stack holds elements in an array-list
@@ -113,7 +113,19 @@ func (stack *Stack) Iterator() Iterator {
 // If Next() returns true, then next element's index and value can be retrieved by Index() and Value().
 // Modifies the state of the iterator.
 func (iterator *Iterator) Next() bool {
-	iterator.index++
+	if iterator.index < iterator.stack.Size() {
+		iterator.index++
+	}
+	return iterator.stack.withinRange(iterator.index)
+}
+
+// Prev moves the iterator to the previous element and returns true if there was a previous element in the container.
+// If Prev() returns true, then previous element's index and value can be retrieved by Index() and Value().
+// Modifies the state of the iterator.
+func (iterator *Iterator) Prev() bool {
+	if iterator.index >= 0 {
+		iterator.index--
+	}
 	return iterator.stack.withinRange(iterator.index)
 }
 

stacks/arraystack/arraystack_test.go

@@ -98,9 +98,11 @@ func TestStackIterator(t *testing.T) {
 	stack.Push("b")
 	stack.Push("c")
 
-	// Iterator
+	// Iterator (next)
 	it := stack.Iterator()
+	count := 0
 	for it.Next() {
+		count++
 		index := it.Index()
 		value := it.Value()
 		switch index {
@@ -119,7 +121,44 @@ func TestStackIterator(t *testing.T) {
 		default:
 			t.Errorf("Too many")
 		}
+		if actualValue, expectedValue := index, count-1; actualValue != expectedValue {
+			t.Errorf("Got %v expected %v", actualValue, expectedValue)
+		}
+	}
+	if actualValue, expectedValue := count, 3; actualValue != expectedValue {
+		t.Errorf("Got %v expected %v", actualValue, expectedValue)
 	}
+
+	// Iterator (prev)
+	count = 0
+	for it.Prev() {
+		count++
+		index := it.Index()
+		value := it.Value()
+		switch index {
+		case 0:
+			if actualValue, expectedValue := value, "c"; actualValue != expectedValue {
+				t.Errorf("Got %v expected %v", actualValue, expectedValue)
+			}
+		case 1:
+			if actualValue, expectedValue := value, "b"; actualValue != expectedValue {
+				t.Errorf("Got %v expected %v", actualValue, expectedValue)
+			}
+		case 2:
+			if actualValue, expectedValue := value, "a"; actualValue != expectedValue {
+				t.Errorf("Got %v expected %v", actualValue, expectedValue)
+			}
+		default:
+			t.Errorf("Too many")
+		}
+		if actualValue, expectedValue := index, 3-count; actualValue != expectedValue {
+			t.Errorf("Got %v expected %v", actualValue, expectedValue)
+		}
+	}
+	if actualValue, expectedValue := count, 3; actualValue != expectedValue {
+		t.Errorf("Got %v expected %v", actualValue, expectedValue)
+	}
+
 	stack.Clear()
 	it = stack.Iterator()
 	for it.Next() {

stacks/linkedliststack/linkedliststack_test.go

@@ -100,7 +100,9 @@ func TestStackIterator(t *testing.T) {
 
 	// Iterator
 	it := stack.Iterator()
+	count := 0
 	for it.Next() {
+		count++
 		index := it.Index()
 		value := it.Value()
 		switch index {
@@ -119,7 +121,14 @@ func TestStackIterator(t *testing.T) {
 		default:
 			t.Errorf("Too many")
 		}
+		if actualValue, expectedValue := index, count-1; actualValue != expectedValue {
+			t.Errorf("Got %v expected %v", actualValue, expectedValue)
+		}
+	}
+	if actualValue, expectedValue := count, 3; actualValue != expectedValue {
+		t.Errorf("Got %v expected %v", actualValue, expectedValue)
 	}
+
 	stack.Clear()
 	it = stack.Iterator()
 	for it.Next() {