Add 2345 Score to output

2 files changed, 56 insertions, 0 deletions

diff --git a/factors/factors_test.go b/factors/factors_test.go
index ceaf4d1..f14dd31 100644
--- a/factors/factors_test.go
+++ b/factors/factors_test.go
@@ -105,6 +105,23 @@ func TestFactorScore(t *testing.T) {
 	}
 }
 
+var basicRankCases = map[uint]string{
+	2: "D-", 3: "E-", 4: "C~", 5: "F+", 6: "B~",
+	7: "F-", 8: "C-", 9: "E~", 10: "D+", 11: "F~", 12: "A-",
+	14: "D~", 15: "E+", 18: "B-", 20: "C+", 24: "A~", 30: "B+", 60: "A+",
+}
+
+func TestBasicRank (t *testing.T) {
+	for i, expected := range basicRankCases {
+		t.Run(fmt.Sprintf("%d", i), func(t *testing.T) {
+			actual := BasicRank(i)
+			if expected != actual {
+				t.Errorf("BasicRank(%d) = %s, want %s", i, actual, expected)
+			}
+		})
+	}
+}
+
 func mapEquals[K comparable, V comparable](a, b map[K]V) bool {
 	for k := range a {
 		if a[k] != b[k] {
diff --git a/factors/score.go b/factors/score.go
index 707120d..b47aac4 100644
--- a/factors/score.go
+++ b/factors/score.go
@@ -26,3 +26,42 @@ func Score(n uint) float64 {
 	}
 	return float64(factorSum) / float64(n)
 }
+
+// BasicRank returns a rank describing how well a base handles the simplest
+// fractions (1/2, 1/3, 1/4 and 1/5)
+// also known as 2345 Rank
+func BasicRank(n uint) string {
+	var firstRank, secondRank string
+	if n%2 == 0 {
+		if n%3 == 0 {
+			if n%4 == 0 {
+				firstRank = "A"
+			} else {
+				firstRank = "B"
+			}
+		} else {
+			if n%4 == 0 {
+				firstRank = "C"
+			} else {
+				firstRank = "D"
+			}
+		}
+	} else {
+		if n%3 == 0 {
+			firstRank = "E"
+		} else {
+			firstRank = "F"
+		}
+	}
+
+	switch n % 5 {
+	case 0:
+		secondRank = "+"
+	case 1, 4:
+		secondRank = "~"
+	case 2, 3:
+		secondRank = "-"
+	}
+
+	return firstRank + secondRank
+}