functions to determine if point is on line

also includes lineOnLine to determine if a line is on another line.
Added a new type line struct which consists of two points.

point.go

@@ -6,6 +6,28 @@ type Point struct {
 	X, Y float64
 }
 
+type line struct {
+	pt1, pt2 Point
+}
+
 func distance(p1, p2 Point) float64 {
 	return math.Sqrt(math.Pow((p1.X-p2.X), 2) + math.Pow((p1.Y-p2.Y), 2))
 }
+
+func onLine(rp1, rp2, p Point) bool {
+	if distance(rp1, p)+distance(rp2, p) == distance(rp1, rp2) {
+		minx, maxx := math.Min(rp1.X, rp2.X), math.Max(rp1.X, rp2.X)
+		miny, maxy := math.Min(rp1.Y, rp2.Y), math.Max(rp1.Y, rp2.Y)
+		if minx <= p.X && p.X <= maxx && miny <= p.Y && p.Y <= maxy {
+			return true
+		}
+	}
+	return false
+}
+
+func lineOnLine(l1, l2 line) bool {
+	if onLine(l1.pt1, l1.pt2, l2.pt1) && onLine(l1.pt1, l1.pt2, l2.pt2) {
+		return true
+	}
+	return false
+}

point_test.go

@@ -27,3 +27,26 @@ func TestDistance(t *testing.T) {
 
 	}
 }
+
+func TestOnLine(t *testing.T) {
+	var onLineTest = []struct {
+		p        []Point
+		expected bool
+	}{
+		{[]Point{Point{1, 1}, Point{3, 3}, Point{2, 2}}, true},
+		{[]Point{Point{1, 1}, Point{3, 3}, Point{4, 4}}, false},
+		{[]Point{Point{-1, -1}, Point{-3, -3}, Point{-4, -4}}, false},
+		{[]Point{Point{-1, -1}, Point{-3, -3}, Point{-2, -2}}, true},
+	}
+	for _, rt := range onLineTest {
+		actual := onLine(rt.p[0], rt.p[1], rt.p[2])
+		if actual != rt.expected {
+			t.Errorf(
+				"failed spiral:\n\texpected: %d\n\t  actual: %d",
+				rt.expected,
+				actual,
+			)
+		}
+
+	}
+}