Create a function that sort letters and prints frequency

03_letters/hsy3418/main.go

@@ -0,0 +1,34 @@
+package main
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"sort"
+	"strings"
+)
+
+var out io.Writer = os.Stdout
+
+//letters is a function returns a mapping of each letter to its frequency.
+func letters(s string) map[rune]int {
+	m := make(map[rune]int)
+	for _, r := range s {
+		m[r]++
+	}
+	return m
+}
+
+//sorLetters is a function returns a sorted slice of strings with elements
+func sortLetters(m map[rune]int) []string {
+	sortSlices := make([]string, 0, len(m))
+	for key, val := range m {
+		sortSlices = append(sortSlices, fmt.Sprintf("%c:%d", key, val))
+	}
+	sort.Strings(sortSlices)
+	return sortSlices
+}
+
+func main() {
+	fmt.Fprintln(out, strings.Join(sortLetters(letters("aba")), "\n"))
+}

03_letters/hsy3418/main_test.go

@@ -0,0 +1,65 @@
+package main
+
+import (
+	"bytes"
+	"strconv"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+var letterTests = []struct {
+	input string
+	want  map[rune]int
+}{
+	{input: "abcdefghijk",
+		want: map[rune]int{'a': 1, 'b': 1, 'c': 1, 'd': 1, 'e': 1, 'f': 1, 'g': 1, 'h': 1, 'i': 1, 'j': 1, 'k': 1}},
+	{input: "894431kdk",
+		want: map[rune]int{'8': 1, '9': 1, '4': 2, '3': 1, '1': 1, 'k': 2, 'd': 1}},
+	{input: "好好学习天天向上",
+		want: map[rune]int{'好': 2, '学': 1, '习': 1, '天': 2, '向': 1, '上': 1}},
+	{input: "🏦🔫🗯💰😬🚓🚓🚓🚓",
+		want: map[rune]int{'🏦': 1, '🔫': 1, '🗯': 1, '💰': 1, '😬': 1, '🚓': 4}},
+}
+
+var sortletterTests = []struct {
+	input map[rune]int
+	want  []string
+}{
+	{input: map[rune]int{'a': 1, 'b': 1, 'c': 1, 'd': 1, 'e': 1, 'f': 1, 'g': 1, 'h': 1, 'i': 1, 'j': 1, 'k': 1},
+		want: []string{"a:1", "b:1", "c:1", "d:1", "e:1", "f:1", "g:1", "h:1", "i:1", "j:1", "k:1"}},
+	{input: map[rune]int{'8': 1, '9': 1, '4': 2, '3': 1, '1': 1, 'k': 2, 'd': 1},
+		want: []string{"1:1", "3:1", "4:2", "8:1", "9:1", "d:1", "k:2"}},
+	{input: map[rune]int{'好': 2, '学': 1, '习': 1, '天': 2, '向': 1, '上': 1},
+		want: []string{"上:1", "习:1", "向:1", "天:2", "好:2", "学:1"}},
+	{input: map[rune]int{'🏦': 1, '🔫': 1, '🗯': 1, '💰': 1, '😬': 1, '🚓': 4},
+		want: []string{"🏦:1", "💰:1", "🔫:1", "🗯:1", "😬:1", "🚓:4"}},
+}
+
+func TestLetters(t *testing.T) {
+	for _, test := range letterTests {
+		actual := letters(test.input)
+		assert.Equal(t, test.want, actual)
+	}
+}
+
+func TestSortLetters(t *testing.T) {
+	for _, test := range sortletterTests {
+		actual := sortLetters(test.input)
+		assert.Equal(t, test.want, actual)
+	}
+}
+
+func TestMainOutput(t *testing.T) {
+	var buf bytes.Buffer
+	out = &buf
+
+	main()
+
+	expected := strconv.Quote("a:2\nb:1\n")
+	actual := strconv.Quote(buf.String())
+
+	if expected != actual {
+		t.Errorf("Unexpected output in main()\nexpected: %q\nactual: %q", expected, actual)
+	}
+}