feat: Add the fibonacci package.

README.md

@@ -13,6 +13,7 @@ So far, the following exercises have been covered:
 - [Cons, Car, Cdr & co.](./cons) – implements a cons cell and the corresponding functions
 - [Continous maximum](./continuousmax/) – calculates the maximum of a sliding window
 - [Egyptian fractions](./egyptianfractions/) – calculates the "Egyptian Fractions" version of a given fraction
+- [Fibonacci](./fibonacci/) – calculates the n-th Fibonacci number
 - [Floyd](./floyd/) – implements Floyd's cycle-finding "Tortoise and Hare" algorithm
 - [Heap](./heap/) – implements a heap from scratch, without using the built-in `container/heap` package
 - [Markov count](./markovcount/) – figures out how often states are reached by a Markov chain

fibonacci/documentation.go

@@ -0,0 +1,2 @@
+// Package fibonacci calculates the n-th Fibonacci number.
+package fibonacci

fibonacci/fibonacci.go

@@ -0,0 +1,8 @@
+package fibonacci
+
+import "math"
+
+func Fib(n int) int {
+	phi := (1 + math.Sqrt(5)) / 2
+	return int(math.Round(math.Pow(phi, float64(n)) / math.Sqrt(5)))
+}

fibonacci/fibonacci_test.go

@@ -0,0 +1,23 @@
+package fibonacci_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/thenativeweb/codingcircle/fibonacci"
+)
+
+func TestFib(t *testing.T) {
+	assert.Equal(t, 1, fibonacci.Fib(1))
+	assert.Equal(t, 1, fibonacci.Fib(2))
+	assert.Equal(t, 2, fibonacci.Fib(3))
+	assert.Equal(t, 3, fibonacci.Fib(4))
+	assert.Equal(t, 5, fibonacci.Fib(5))
+	assert.Equal(t, 8, fibonacci.Fib(6))
+	assert.Equal(t, 13, fibonacci.Fib(7))
+	assert.Equal(t, 21, fibonacci.Fib(8))
+	assert.Equal(t, 34, fibonacci.Fib(9))
+	assert.Equal(t, 55, fibonacci.Fib(10))
+
+	assert.Equal(t, 1134903170, fibonacci.Fib(45))
+}