- add insert for list and arraylist

README.md

@@ -138,6 +138,7 @@ type Interface interface {
 	Contains(elements ...interface{}) bool
 	Sort(comparator utils.Comparator)
     Swap(index1, index2 int)
+   	Insert(index int, elements ...interface{})
 
 	containers.Interface
 	// Empty() bool
@@ -180,6 +181,8 @@ func main() {
 	_ = list.Size()                       // 0
 	list.Add("a")                         // ["a"]
 	list.Clear()                          // []
+    list.Insert(0, "b")                   // ["b"]
+    list.Insert(0, "a")                   // ["a","b"]
 }
 ```
 

lists/arraylist/arraylist.go

@@ -149,6 +149,32 @@ func (list *List) Swap(i, j int) {
 	}
 }
 
+// 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, elements ...interface{}) {
+
+	if !list.withinRange(index) {
+		// Append
+		if index == list.size {
+			list.Add(elements...)
+		}
+		return
+	}
+
+	l := len(elements)
+	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, element := range elements {
+		list.elements[index+i] = element
+	}
+}
+
 func (list *List) String() string {
 	str := "ArrayList\n"
 	values := []string{}
@@ -161,7 +187,7 @@ func (list *List) String() string {
 
 // Check that the index is withing bounds of the list
 func (list *List) withinRange(index int) bool {
-	return index >= 0 && index < list.size && list.size != 0
+	return index >= 0 && index < list.size
 }
 
 func (list *List) resize(cap int) {

lists/arraylist/arraylist_test.go

@@ -27,6 +27,7 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 package arraylist
 
 import (
+	"fmt"
 	"github.com/emirpasic/gods/utils"
 	"testing"
 )
@@ -120,6 +121,19 @@ func TestArrayList(t *testing.T) {
 		t.Errorf("Got %v expected %v", actualValue, true)
 	}
 
+	list.Insert(0, "h")
+	list.Insert(0, "e")
+	list.Insert(1, "f")
+	list.Insert(2, "g")
+	list.Insert(4, "i")
+	list.Insert(0, "a", "b")
+	list.Insert(list.Size(), "j", "k")
+	list.Insert(2, "c", "d")
+
+	if actualValue, expectedValue := fmt.Sprintf("%s%s%s%s%s%s%s%s%s%s%s", list.Values()...), "abcdefghijk"; actualValue != expectedValue {
+		t.Errorf("Got %v expected %v", actualValue, expectedValue)
+	}
+
 }
 
 func BenchmarkArrayList(b *testing.B) {

lists/lists.go

@@ -30,6 +30,7 @@ type Interface interface {
 	Contains(elements ...interface{}) bool
 	Sort(comparator utils.Comparator)
 	Swap(index1, index2 int)
+	Insert(index int, elements ...interface{})
 
 	containers.Interface
 	// Empty() bool