impl skip list

Author: email2liyang

scala/src/main/scala/ch17_skip_list/SkipList.scala

@@ -0,0 +1,99 @@
+package ch17_skip_list
+
+import scala.util.Random
+
+class Node(var data: Int, var forwards: Array[Node], var maxLevel: Int)
+
+class SkipList(var head: Node, var skipListLevel: Int) {
+
+ def this() = this(new Node(-1, new Array[Node](16), 0), 1)
+
+ val MAX_LEVEL = 16
+ val random = new Random()
+
+ def find(value: Int): Option[Node] = {
+ var p = head
+ for (i <- skipListLevel - 1 to 0 by -1) {
+ while (p.forwards(i) != null && p.forwards(i).data < value) {
+ p = p.forwards(i)
+ }
+ }
+ if (p.forwards(0) != null && p.forwards(0).data == value) {
+ Some(p.forwards(0))
+ } else {
+ None
+ }
+ }
+
+ def insert(value: Int): Unit = {
+ //init the new node
+ val level = randomLevel()
+ val newNode = new Node(value, new Array[Node](level), level)
+
+ //use updtes array to record all nodes in all level before the inserted node
+ val updates: Array[Node] = new Array[Node](level)
+ var p = head
+ for (i <- level - 1 to 0 by -1) {
+ while (p.forwards(i) != null && p.forwards(i).data < value) {
+ p = p.forwards(i)
+ }
+ updates(i) = p
+ }
+
+ for (i <- Range(0, level)) {
+ newNode.forwards(i) = updates(i).forwards(i)
+ updates(i).forwards(i) = newNode
+ }
+
+ if (level > skipListLevel) {
+ skipListLevel = level
+ }
+ }
+
+ def delete(value: Int): Unit = {
+ var p = head
+ val updates: Array[Node] = new Array[Node](skipListLevel)
+
+ //try to locate the given node with the value
+ for (i <- skipListLevel - 1 to 0 by -1) {
+ while (p.forwards(i) != null && p.forwards(i).data < value) {
+ p = p.forwards(i)
+ }
+ updates(i) = p
+ }
+
+ if (p.forwards(0) != null && p.forwards(0).data == value) {
+ //find the value node, start to delete the node from the skip list
+ for (i <- skipListLevel - 1 to 0 by -1) {
+ if (updates(i).forwards(i) != null && updates(i).forwards(i).data == value) {
+ updates(i).forwards(i) = updates(i).forwards(i).forwards(i)
+ }
+ }
+ }
+
+ }
+
+ def randomLevel(): Int = {
+ var level = 1
+ for (i <- Range(1, MAX_LEVEL)) {
+ if (random.nextInt() % 2 == 1) {
+ level += 1
+ }
+ }
+
+ level
+ }
+
+ def mkString(): String = {
+ val builder = new StringBuilder
+ var p = head
+ while (p.forwards(0) != null) {
+ p = p.forwards(0)
+ builder.append(p.data)
+ }
+
+ builder.mkString
+ }
+}
+
+

scala/src/test/scala/ch17_skip_list/SkipListTest.scala

@@ -0,0 +1,44 @@
+package ch17_skip_list
+
+import org.scalatest.{FlatSpec, Matchers}
+
+import scala.util.Random
+
+class SkipListTest extends FlatSpec with Matchers {
+
+ behavior of "SkipListTest"
+
+ it should "insert skip list" in {
+ val list = new SkipList()
+ for (i <- Range(0, 10)) {
+ list.insert(i)
+ }
+
+ list.mkString() should equal("0123456789")
+ }
+
+ it should "delete skip list" in {
+ val list = new SkipList()
+ for (i <- Range(0, 10)) {
+ list.insert(i)
+ }
+
+ list.delete(5)
+ list.mkString() should equal("012346789")
+ }
+
+ it should "find value in skip list" in {
+ val list = new SkipList()
+ val length = 5000
+ val array = new Array[Int](length)
+ val rnd = new Random()
+ for (i <- Range(0, length)) {
+ array(i) = rnd.nextInt(length)
+ list.insert(array(i))
+ }
+
+ assert(list.find(array(rnd.nextInt(length - 1))).isDefined)
+ assert(list.find(array(rnd.nextInt(length - 1)) + length + 1).isEmpty)
+
+ }
+}