- add insert for doublylinkedlist

README.md

@@ -255,6 +255,8 @@ func main() {
 	_ = list.Size()                       // 0
 	list.Add("a")                         // ["a"]
 	list.Clear()                          // []
+    list.Insert(0, "b")                   // ["b"]
+    list.Insert(0, "a")                   // ["a","b"]
 }
 ```
 

lists/doublylinkedlist/doublylinkedlist.go

@@ -244,6 +244,60 @@ 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, values ...interface{}) {
+
+	if !list.withinRange(index) {
+		// Append
+		if index == list.size {
+			list.Add(values...)
+		}
+		fmt.Println(list.Values())
+		return
+	}
+
+	list.size += len(values)
+
+	var beforeElement *element
+	var foundElement *element
+	// determine traversal direction, last to first or first to last
+	if list.size-index < index {
+		foundElement = list.last
+		for e := list.size - 1; e != index; e, foundElement = e-1, foundElement.prev {
+			beforeElement = foundElement.prev
+		}
+	} else {
+		foundElement = list.first
+		for e := 0; e != index; e, foundElement = e+1, foundElement.next {
+			beforeElement = foundElement
+		}
+	}
+
+	if foundElement == list.first {
+		oldNextElement := list.first
+		for i, value := range values {
+			newElement := &element{value: value}
+			if i == 0 {
+				list.first = newElement
+			} else {
+				beforeElement.next = newElement
+			}
+			beforeElement = newElement
+		}
+		beforeElement.next = oldNextElement
+	} else {
+		oldNextElement := beforeElement.next
+		for _, value := range values {
+			newElement := &element{value: value}
+			beforeElement.next = newElement
+			beforeElement = newElement
+		}
+		beforeElement.next = oldNextElement
+	}
+}
+
 func (list *List) String() string {
 	str := "DoublyLinkedList\n"
 	values := []string{}

lists/doublylinkedlist/doublylinkedlist_test.go

@@ -27,6 +27,7 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 package doublylinkedlist
 
 import (
+	"fmt"
 	"github.com/emirpasic/gods/utils"
 	"testing"
 )
@@ -122,6 +123,19 @@ func TestDoublyLinkedList(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 BenchmarkDoublyLinkedList(b *testing.B) {