impl ch10 recursive

scala/src/main/scala/ch10_recursive/RecursiveDemo.scala

@@ -0,0 +1,23 @@
+package ch10_recursive
+
+import scala.collection.mutable
+
+object RecursiveDemo {
+
+  def calculateStepWays(steps: Int): Int = {
+    //use knownResults to avoid duplicated computing
+    val knownResults = mutable.HashMap.empty[Int, Int]
+    steps match {
+      case 1 => 1
+      case 2 => 2
+      case _ => knownResults.get(steps) match {
+        case Some(result) => result
+        case None => {
+          val result = calculateStepWays(steps - 1) + calculateStepWays(steps - 2)
+          knownResults.put(steps, result)
+          result
+        }
+      }
+    }
+  }
+}

scala/src/test/scala/ch10_recursive/RecursiveDemoTest.scala

@@ -0,0 +1,17 @@
+package ch10_recursive
+
+import org.scalatest.{FlatSpec, Matchers}
+
+class RecursiveDemoTest extends FlatSpec with Matchers {
+
+  behavior of "RecursiveDemoTest"
+
+  it should "calculateStepWays" in {
+    RecursiveDemo.calculateStepWays(1) should equal(1)
+    RecursiveDemo.calculateStepWays(2) should equal(2)
+    RecursiveDemo.calculateStepWays(3) should equal(3)
+    RecursiveDemo.calculateStepWays(4) should equal(5)
+    RecursiveDemo.calculateStepWays(5) should equal(8)
+  }
+
+}