WIP: working on add element by index

Author: MuhammadZohair

src/kotlin_lang/Main.kt

@@ -12,4 +12,11 @@ fun main() {
 //    singlyLinkedList.add("Awais")
 //    println(singlyLinkedList.copyToString())
 
+    println("Hello, world!!!")
+
+    val list: java.util.LinkedList<Int> = java.util.LinkedList<Int>()
+
+    list.add(0)
+    list.add(1, 1)
+
 }

src/kotlin_lang/lists/Collection.kt

@@ -3,6 +3,7 @@ package kotlin_lang.lists
 interface Collection<T> {
 
     fun add(element: T): Boolean
+    fun add(index: Int, element: T)
 
 
 }

src/kotlin_lang/lists/singly_linked_list/SinglyLinkedList.kt

@@ -6,6 +6,7 @@ import kotlin_lang.lists.Collection
 class SinglyLinkedList<T> : Collection<T> {
 
     var head: Node<T>? = null
+    var sizeOfList: Int = 0
 
     override fun add(element: T): Boolean {
         head?.let {
@@ -14,12 +15,23 @@ class SinglyLinkedList<T> : Collection<T> {
                 currentNode = currentNode.nextRef!!
             }
             currentNode.nextRef = Node(element, null)
+            sizeOfList++
             return true
         } ?: run {
             head = Node(element, null)
+            sizeOfList++
             return true
         }
     }
 
+    override fun add(index: Int, element: T) {
+        if (index > sizeOfList) throw IndexOutOfBoundsException("Index not accessible")
+
+        head?.let {
+            head = Node(element, null)
+        }
+
+    }
+
     data class Node<T>(var info: T, var nextRef: Node<T>?)
 }

src/kotlin_lang/lists/singly_linked_list/SinglyLinkedListTest.kt

@@ -1,6 +1,7 @@
 package kotlin_lang.lists.singly_linked_list
 
 import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Assertions.assertThrows
 import org.junit.jupiter.api.BeforeEach
 import org.junit.jupiter.api.Test
 
@@ -37,5 +38,35 @@ class SinglyLinkedListTest {
         assertEquals(2, linkedList.head?.nextRef?.nextRef?.info)
     }
 
+    @Test
+    fun addByIndex_listIsEmpty_elementAddedToHead() {
+        linkedList.add(0, 0)
+        assertEquals(0, linkedList.head?.info)
+    }
+
+    @Test
+    fun addByIndex_listIsEmpty_indexInRange_elementAddedToHead() {
+
+        linkedList.add(0, 2)
+        assertEquals(2, linkedList.head?.info)
+    }
+
+    @Test
+    fun addByIndex_listNotEmpty_indexInRange_elementAddedToHead() {
+
+        linkedList.add(0, 1)
+        linkedList.add(1, 2)
+        linkedList.add(2, 3)
+        assertEquals(3, linkedList.head?.nextRef?.nextRef?.info)
+    }
+
+    @Test
+    fun addByIndex_indexOutOfRange_throwsException() {
+        assertThrows(IndexOutOfBoundsException::class.java) {
+            linkedList.add(4, 1)
+        }
+
+    }
+
 
 }