implement secretmessage, test multibyte unicode

secretmessage/secretmessage.go

@@ -1,6 +1,47 @@
 package secretmessage
 
-// Decode func
+import (
+	"sort"
+	"strings"
+)
+
+// pair tracks frequency of a character
+type pair struct {
+	c string
+	n int
+}
+
+// Decode sorts encoded by descending rune frequency, discards all but one of each rune, then returns everything before "_"
 func Decode(encoded string) string {
-	return ""
+	var (
+		chars = strings.Split(encoded, "")
+		m     = make(map[string]int)
+		s     = make([]pair, 1)
+		out   = ""
+		i     = -1
+	)
+
+	// count frequencies:
+	for _, c := range chars {
+		m[c]++
+	}
+
+	// Order the runes by descending frequency:
+	for k, v := range m {
+		s = append(s, pair{c: k, n: v})
+	}
+	sort.Slice(s, func(i, j int) bool {
+		return s[i].n > s[j].n
+	})
+
+	// Append each character to `out` until we reach _:
+	for {
+		i++
+		if s[i].c == "_" {
+			break
+		}
+		out += s[i].c
+	}
+
+	return out
 }

secretmessage/secretmessage_test.go

@@ -19,3 +19,17 @@ func BenchmarkDecode(b *testing.B) {
 		Decode(encoded)
 	}
 }
+
+func TestDecodeSimple(t *testing.T) {
+	actual := Decode("b_bcb_")
+	if actual != "b" {
+		t.Fatalf("Expected %s, got %s", "b", actual)
+	}
+}
+
+func TestDecodeSimpleMultibyteUnicode(t *testing.T) {
+	actual := Decode("Ƃ_ƂcƂ_")
+	if actual != "Ƃ" {
+		t.Fatalf("Expected %s, got %s", "Ƃ", actual)
+	}
+}