add Clear() method to stack interface

stacks/arraystack/arraystack.go

@@ -88,6 +88,12 @@ func (stack *Stack) Size() int {
 	return stack.top + 1
 }
 
+// Removes all elements from the stack.
+func (stack *Stack) Clear() {
+	stack.top = -1
+	stack.items = []interface{}{}
+}
+
 func (stack *Stack) String() string {
 	str := "ArrayStack\n"
 	values := []string{}

stacks/linkedliststack/linkedliststack.go

@@ -84,6 +84,12 @@ func (stack *Stack) Size() int {
 	return stack.size
 }
 
+// Removes all elements from the stack.
+func (stack *Stack) Clear() {
+	stack.top = nil
+	stack.size = 0
+}
+
 func (stack *Stack) String() string {
 	str := "LinkedListStack\n"
 	element := stack.top

stacks/stacks.go

@@ -24,4 +24,5 @@ type Interface interface {
 	Peek() (value interface{}, ok bool)
 	Empty() bool
 	Size() int
+	Clear()
 }