complete checkCircle and reserve

scala/src/main/scala/ch07_linkedlist/LinkedListAlgo.scala

@@ -0,0 +1,58 @@
+package ch07_linkedlist
+
+import ch06_linkedlist.Node
+
+object LinkedListAlgo {
+
+  //reverse a linked list
+  def reverse(head: Node): Node = {
+    if (head.next.isEmpty) {
+      //single node of linked list
+      return head
+    }
+    var prev: Option[Node] = None
+    var current: Option[Node] = Some(head)
+    var next: Option[Node] = None
+
+    while (current.get.next.isDefined) {
+      next = current.get.next
+      current.get.next = prev
+
+      prev = current
+      current = next
+    }
+    //for the tail of the node, make it point to previous node to complete the reverse
+    current.get.next = prev
+
+    current.get
+  }
+
+  def checkCircle(head: Node): Boolean = {
+    var fast = head
+    var slow = head
+
+    while (fast.next.isDefined && fast.next.get.next.isDefined) {
+      fast = fast.next.get.next.get
+      slow = slow.next.get
+
+      if (fast.equals(slow)) {
+        return true
+      }
+    }
+    false
+  }
+
+  //form all the chain value as string
+  def mkStringForChain(node: Node): String = {
+    val result = new StringBuilder
+
+    var p = node
+
+    while (p.next.isDefined) {
+      result.append(p.data)
+      p = p.next.get
+    }
+    result.append(p.data)
+    result.mkString
+  }
+}

scala/src/test/scala/ch07_linkedlist/LinkedListAlgoTest.scala

@@ -0,0 +1,76 @@
+package ch07_linkedlist
+
+import ch06_linkedlist.{Node, SinglyLinkedList}
+import org.scalatest.{FlatSpec, Matchers}
+
+class LinkedListAlgoTest extends FlatSpec with Matchers {
+
+  behavior of "LinkedListAlgoTest"
+
+  it should "reverse a node for long linked list" in {
+    val list = new SinglyLinkedList()
+
+    for (i <- 0 to 9) {
+      list.insertTail(i)
+    }
+    LinkedListAlgo.mkStringForChain(list.headOpt.get) should equal((0 to 9).toArray.mkString(""))
+
+    val reverseNode = LinkedListAlgo.reverse(list.headOpt.get)
+
+    LinkedListAlgo.mkStringForChain(reverseNode) should equal((9 to 0 by -1).toArray.mkString(""))
+  }
+
+  it should "reverse a node for linked list with 1 node" in {
+    val list = new SinglyLinkedList()
+
+    list.insertTail(100)
+
+    LinkedListAlgo.mkStringForChain(list.headOpt.get) should equal("100")
+
+    val reverseNode = LinkedListAlgo.reverse(list.headOpt.get)
+
+    LinkedListAlgo.mkStringForChain(reverseNode) should equal("100")
+  }
+
+  it should "check circle for circled linked list" in {
+
+    val node1 = new Node(1, None)
+    val node2 = new Node(2, None)
+    val node3 = new Node(3, None)
+    val node4 = new Node(4, None)
+    val node5 = new Node(5, None)
+    val node6 = new Node(6, None)
+
+    //1->2->3->4->5->6->3 it's a circle
+    //node1 is the head
+    node1.next = Some(node2)
+    node2.next = Some(node3)
+    node3.next = Some(node4)
+    node4.next = Some(node5)
+    node5.next = Some(node6)
+    node6.next = Some(node3)
+
+    assert(LinkedListAlgo.checkCircle(node1))
+  }
+
+  it should "check circle for none circled linked list" in {
+
+    val node1 = new Node(1, None)
+    val node2 = new Node(2, None)
+    val node3 = new Node(3, None)
+    val node4 = new Node(4, None)
+    val node5 = new Node(5, None)
+    val node6 = new Node(6, None)
+
+    //1->2->3->4->5->6->null it's not a circle
+    //node1 is the head
+    node1.next = Some(node2)
+    node2.next = Some(node3)
+    node3.next = Some(node4)
+    node4.next = Some(node5)
+    node5.next = Some(node6)
+
+    assert(!LinkedListAlgo.checkCircle(node1))
+  }
+
+}