add fibonacci alg

.gitignore

@@ -1,5 +1,5 @@
 .DS_Store
-.idea/shelf
+.idea
 /android.tests.dependencies
 /confluence/target
 /dependencies/repo

src/main/kotlin/dynamicProgramming/Fibonacci.kt

@@ -0,0 +1,32 @@
+package dynamicProgramming
+
+/**
+ * The following example is taken from Ken Kousen book "Kotlin Cookbook. A Problem-Focused Approach"
+ */
+
+/**
+ * Get Fibonacci sequence
+ */
+fun fibonacciSequence() = sequence {
+    var terms = Pair(0, 1)
+    while (true) {
+        yield(terms.first)
+        terms = terms.second to terms.first + terms.second
+    }
+}
+
+
+/**
+ * Get n Fibonacci number
+ */
+fun fibonacciFold(n: Int) =
+    (2 until n).fold(1 to 1) { (prev, curr), _ ->
+        curr to (prev + curr) }.second
+
+/**
+ * Get n Fibonacci number
+ */
+@JvmOverloads
+tailrec fun fibonacci(n: Int, a: Int = 0, b: Int = 1): Int =
+    when (n) { 0 -> a 1 -> b
+        else -> fibonacci(n - 1, b, a + b) }