Added three algorithms for calculating nth Fibbonacci number

src/main/scala/Others/Fibbonacci.scala

@@ -0,0 +1,46 @@
+package Others
+
+import scala.annotation.tailrec
+
+/**
+  * Assuming that sequence starts from 0
+  */
+object Fibbonacci {
+  /**
+    * Standard recursion solution,
+    *
+    * @param n - which Fibbonacci number
+    * @return
+    */
+  def nthNumberRecursive(n: Int): Int = {
+    if (n <= 1) 1
+    else nthNumberRecursive(n - 1) + nthNumberRecursive(n - 2)
+  }
+
+  def nthNumberIterative(n: Int): Int = {
+    var first = 1
+    var second = 1
+    if (n == 0) first
+    else if (n == 1) second
+    else {
+      var third: Int = first + second
+      for (i <- 3 to n) {
+        first = second
+        second = third
+        third = first + second
+      }
+      third
+    }
+  }
+
+  def nthNumberTailRec(n: Int): Int = {
+    @tailrec
+    def nthNumber(n: Int, current: Int, temp: Int): Int = n match {
+      case 0 => current
+      case _ => nthNumber(n - 1, temp, current + temp)
+    }
+
+    nthNumber(n, 1, 1)
+  }
+
+}

src/test/scala/Others/FibbonacciSpec.scala

@@ -0,0 +1,42 @@
+package Others
+
+import org.scalatest.FlatSpec
+
+class FibbonacciSpec extends FlatSpec {
+
+  "recursive solution" should "start from 1" in {
+    assert(Fibbonacci.nthNumberRecursive(0) === 1)
+  }
+
+  it should "calculate some fibbonacci number" in {
+    assert(Fibbonacci.nthNumberRecursive(4) === 5)
+  }
+
+  it should "return sum of two previous numbers" in {
+    for (i <- 2 to 10) assert(Fibbonacci.nthNumberRecursive(i) === Fibbonacci.nthNumberRecursive(i - 1) + Fibbonacci.nthNumberRecursive(i - 2))
+  }
+
+  "iterative solution" should "start from 1" in {
+    assert(Fibbonacci.nthNumberIterative(0) === 1)
+  }
+
+  it should "calculate some fibbonacci number" in {
+    assert(Fibbonacci.nthNumberIterative(4) === 5)
+  }
+
+  it should "return sum of two previous numbers" in {
+    for (i <- 2 to 20) assert(Fibbonacci.nthNumberIterative(i) === Fibbonacci.nthNumberIterative(i - 1) + Fibbonacci.nthNumberIterative(i - 2))
+  }
+
+  "tail recursive solution" should "start from 1" in {
+    assert(Fibbonacci.nthNumberTailRec(0) === 1)
+  }
+
+  it should "calculate some fibbonacci number" in {
+    assert(Fibbonacci.nthNumberTailRec(4) === 5)
+  }
+
+  it should "return sum of two previous numbers" in {
+    for (i <- 2 to 20) assert(Fibbonacci.nthNumberTailRec(i) === Fibbonacci.nthNumberTailRec(i - 1) + Fibbonacci.nthNumberTailRec(i - 2))
+  }
+}