Create 0707-design-linked-list.kt

Author: a93a

Diff for: kotlin/0707-design-linked-list.kt

@@ -0,0 +1,92 @@
+class MyLinkedList() {
+
+    class ListNode(var `val`: Int) {
+        var next: ListNode? = null
+        var prev: ListNode? = null
+    }
+
+    val head = ListNode(0)
+    val tail = ListNode(0)
+    
+    init {
+        head.next = tail
+        tail.prev = head
+    }
+
+    fun get(index: Int): Int {
+        var current = head.next
+        var i = 0
+        while( current != null && i != index) {
+            current = current.next
+            i++
+        }
+        return if(current != null && current != tail) current.`val` else -1
+    }
+
+    fun addAtHead(`val`: Int) {
+        val prev = head
+        val next = head.next
+        val new = ListNode(`val`)
+
+        head.next = new
+        new.prev = head
+        new.next = next
+        next?.prev = new
+    }
+
+    fun addAtTail(`val`: Int) {
+        val next = tail
+        val prev = tail.prev
+        val new = ListNode(`val`)
+
+        tail.prev = new
+        new.prev = prev
+        new.next = tail
+        prev?.next = new
+    }
+
+    fun addAtIndex(index: Int, `val`: Int) {
+        var current = head.next
+        var i = 0
+        while( current != null && i != index) {
+            current = current.next
+            i++
+        }
+        if(current != null) {
+            val prev = current.prev
+            val new = ListNode(`val`)
+
+            prev?.next = new
+            new.prev = prev
+            new.next = current
+            current.prev = new
+        }
+    }
+
+    fun deleteAtIndex(index: Int) {
+        var current = head.next
+        var i = 0
+        while( current != null && i != index) {
+            current = current.next
+            i++
+        }
+        if(current != null && current != tail) {
+            val prev = current.prev
+            val next = current.next
+
+            prev?.next = next
+            next?.prev = prev
+        }
+    }
+
+}
+
+/**
+ * Your MyLinkedList object will be instantiated and called as such:
+ * var obj = MyLinkedList()
+ * var param_1 = obj.get(index)
+ * obj.addAtHead(`val`)
+ * obj.addAtTail(`val`)
+ * obj.addAtIndex(index,`val`)
+ * obj.deleteAtIndex(index)
+ */