Kotlin - LinkedList complete

kotlin/linked-list/src/main/kotlin/Deque.kt

@@ -1,61 +1,101 @@
 class Deque<T> {
-    var firstNode: Node<T>? = null
-    var lastNode: Node<T>? = null
 
-    // Remove value at back
-    fun pop(): T{
-        val returnData = lastNode!!.data
-        lastNode = lastNode?.beforeNode
-        return returnData
-    }
+    private var head:Node<T>? = null
 
-    // Add value at back
-    fun push(elem: T): Unit {
-        if (firstNode == null) {
-            firstNode = Node<T>(data = elem, beforeNode = null, afterNode = null)
+    fun first():Node<T>? = head
+
+    fun last(): Node<T>? {
+        var node = head
+        if (node != null){
+            while (node?.next != null) {
+                node = node.next
+            }
+            return node
         } else {
-            if (lastNode == null){
-                this.lastNode = Node<T>(data = elem, beforeNode = firstNode, afterNode = null)
-                firstNode?.linkBefore(this.lastNode!!)
-            }
-            else {
-                this.lastNode?.linkBefore(Node<T>(data = elem, beforeNode = this.lastNode, afterNode = null))
-            }
+            return null
         }
     }
 
-    // Remove value at front
-    fun shift(): T{
-        val returnData = firstNode!!.data
-        firstNode = firstNode?.afterNode
-        return returnData
+    fun nodeAtIndex(index: Int) : Node<T>? {
+        if (index >= 0) {
+            var node = head
+            var i = index
+            while (node != null) {
+                if (i == 0) return node
+                i -= 1
+                node = node.next
+            }
+        }
+        return null
     }
 
-    // Add value at front
-    fun unshift(elem: T): Unit {
-        if (firstNode == null) {
-            firstNode = Node<T>(data = elem, beforeNode = null, afterNode = null)
+    fun push(value: T) {
+        val newNode = Node(value)
+
+        val lastNode = this.last()
+        if (lastNode != null) {
+            newNode.previous = lastNode
+            lastNode.next = newNode
         } else {
-            if (lastNode == null){
-                this.lastNode = this.firstNode
-                firstNode = Node<T>(data = elem, beforeNode = null, afterNode = this.lastNode)
-                this.lastNode?.linkAfter(firstNode!!)
-            }
-            else {
-                this.firstNode?.linkAfter(Node<T>(data = elem, beforeNode = null, afterNode = this.firstNode))
-            }
+            head = newNode
+        }
+    }
+
+    fun unshift(value: T) {
+        val newNode = Node(value)
+
+        val firstNode = this.first()
+        if (firstNode != null){
+            newNode.next = firstNode
+            firstNode.previous = newNode
+            head = newNode
+        } else {
+            head = newNode
+        }
+    }
+
+    fun removeNode(node: Node<T>):T {
+        val prev = node.previous
+        val next = node.next
+
+        if (prev != null) {
+            prev.next = next
+        } else {
+            head = next
+        }
+        next?.previous = prev
+
+        node.previous = null
+        node.next = null
+
+        return node.value
+    }
+
+    fun pop() : T? {
+        val last = this.last()
+        if (last != null) {
+            return removeNode(last)
+        } else {
+            return null
+        }
+    }
+
+    fun shift(): T? {
+        return removeAtIndex(0)
+    }
+
+    fun removeAtIndex(index: Int):T? {
+        val node = nodeAtIndex(index)
+        if (node != null) {
+            return removeNode(node)
+        } else {
+            return null
         }
     }
 }
 
-data class Node<R>(val data: R, var beforeNode: Node<R>?, var afterNode: Node<R>?) {
-    fun linkBefore(afterNode: Node<R>): Unit {
-        this.afterNode = afterNode
-        afterNode.beforeNode = this
-    }
-
-    fun linkAfter(beforeNode: Node<R>): Unit {
-        this.beforeNode = beforeNode
-        beforeNode.afterNode = this
-    }
+class Node<T>(value: T){
+    var value:T = value
+    var next: Node<T>? = null
+    var previous:Node<T>? = null
 }