Added Pythagoras Theorem (#205)

* Added Pythagoras Theorem

* Removed Main, changed package name

* Exported Vector Struct for external use

* TableDriven Test, better float64 handling

* Parallel Testing, fixed leftover math.Abs function

Author: localleon

math/pythagoras/pythagoras.go

@@ -0,0 +1,18 @@
+package pythagoras
+
+import (
+	"math"
+)
+
+//Vector defines a tuple with 3 values in 3d-space
+type Vector struct {
+	x float64
+	y float64
+	z float64
+}
+
+//Distance calculates the distance between to vectors with the   Pythagoras theorem
+func Distance(a, b Vector) float64 {
+	res := math.Pow(b.x-a.x, 2.0) + math.Pow(b.y-a.y, 2.0) + math.Pow(b.z-a.z, 2.0)
+	return math.Sqrt(res)
+}

math/pythagoras/pythagoras_test.go

@@ -0,0 +1,37 @@
+package pythagoras
+
+import (
+	"math"
+	"testing"
+)
+
+// TableDrivenTest for checking multiple values against our Test Function
+var distanceTest = []struct {
+	name string
+	v1   Vector
+	v2   Vector
+	res  float64
+}{
+	{"random negative vector", Vector{2, -1, 7}, Vector{1, -3, 5}, 3.0},
+	{"random wide vectors", Vector{4, 10, 9}, Vector{4, 3, 5}, 8.06},
+	{"random wide vectors", Vector{8, 5, 5}, Vector{1, 1, 12}, 10.67},
+	{"random short vectors", Vector{1, 1, 1}, Vector{2, 2, 2}, 1.73},
+}
+
+//TestDistance tests the Function Distance with 2 vectors
+func TestDistance(t *testing.T) {
+	t.Parallel() // marks TestDistance as capable of running in parallel with other tests
+	for _, tt := range distanceTest {
+		tt := tt // NOTE: https://github.com/golang/go/wiki/CommonMistakes#using-goroutines-on-loop-iterator-variables
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			res := Distance(tt.v1, tt.v2)           // Calculate result for
+			roundRes := (math.Floor(res*100) / 100) // Round to 2 decimal places because we can't compare an infinite number of places
+			// Check result
+			if roundRes != tt.res {
+				t.Errorf("Distance(%v, %v) = %f, expected %f",
+					tt.v1, tt.v2, roundRes, tt.res)
+			}
+		})
+	}
+}