From f5aeb9af01aa1b4b5ba2becccd8e7cb1a3fe365d Mon Sep 17 00:00:00 2001
From: ivan <ivan.li@practiceinsight.io>
Date: Wed, 19 Dec 2018 15:25:10 +0800
Subject: [PATCH] impl ch10 recursive

---
 .../scala/ch10_recursive/RecursiveDemo.scala  | 23 +++++++++++++++++++
 .../ch10_recursive/RecursiveDemoTest.scala    | 17 ++++++++++++++
 2 files changed, 40 insertions(+)
 create mode 100644 scala/src/main/scala/ch10_recursive/RecursiveDemo.scala
 create mode 100644 scala/src/test/scala/ch10_recursive/RecursiveDemoTest.scala

diff --git a/scala/src/main/scala/ch10_recursive/RecursiveDemo.scala b/scala/src/main/scala/ch10_recursive/RecursiveDemo.scala
new file mode 100644
index 0000000..50613eb
--- /dev/null
+++ b/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
+        }
+      }
+    }
+  }
+}
diff --git a/scala/src/test/scala/ch10_recursive/RecursiveDemoTest.scala b/scala/src/test/scala/ch10_recursive/RecursiveDemoTest.scala
new file mode 100644
index 0000000..1987ece
--- /dev/null
+++ b/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)
+  }
+
+}