Add go/twelve-days

go/twelve-days/README.md

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+# Twelve Days
+
+Output the lyrics to 'The Twelve Days of Christmas'.
+
+```text
+On the first day of Christmas my true love gave to me: a Partridge in a Pear Tree.
+
+On the second day of Christmas my true love gave to me: two Turtle Doves, and a Partridge in a Pear Tree.
+
+On the third day of Christmas my true love gave to me: three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
+
+On the fourth day of Christmas my true love gave to me: four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
+
+On the fifth day of Christmas my true love gave to me: five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
+
+On the sixth day of Christmas my true love gave to me: six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
+
+On the seventh day of Christmas my true love gave to me: seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
+
+On the eighth day of Christmas my true love gave to me: eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
+
+On the ninth day of Christmas my true love gave to me: nine Ladies Dancing, eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
+
+On the tenth day of Christmas my true love gave to me: ten Lords-a-Leaping, nine Ladies Dancing, eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
+
+On the eleventh day of Christmas my true love gave to me: eleven Pipers Piping, ten Lords-a-Leaping, nine Ladies Dancing, eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
+
+On the twelfth day of Christmas my true love gave to me: twelve Drummers Drumming, eleven Pipers Piping, ten Lords-a-Leaping, nine Ladies Dancing, eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree.
+```
+
+## Running the tests
+
+To run the tests run the command `go test` from within the exercise directory.
+
+If the test suite contains benchmarks, you can run these with the `--bench` and `--benchmem`
+flags:
+
+    go test -v --bench . --benchmem
+
+Keep in mind that each reviewer will run benchmarks on a different machine, with
+different specs, so the results from these benchmark tests may vary.
+
+## Further information
+
+For more detailed information about the Go track, including how to get help if
+you're having trouble, please visit the exercism.io [Go language page](http://exercism.io/languages/go/resources).
+
+## Source
+
+Wikipedia [http://en.wikipedia.org/wiki/The_Twelve_Days_of_Christmas_(song)](http://en.wikipedia.org/wiki/The_Twelve_Days_of_Christmas_(song))
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

go/twelve-days/twelve-days.go

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+// Package twelve outputs the lyrics to The Twelve Days of Christmas.
+package twelve
+
+import (
+	"fmt"
+)
+
+var ordinals = [13]string{
+	"zeroth",
+	"first",
+	"second",
+	"third",
+	"fourth",
+	"fifth",
+	"sixth",
+	"seventh",
+	"eighth",
+	"ninth",
+	"tenth",
+	"eleventh",
+	"twelfth",
+}
+
+var gifts = [13]string{
+	"a null pointer",
+	"a Partridge in a Pear Tree",
+	"two Turtle Doves",
+	"three French Hens",
+	"four Calling Birds",
+	"five Gold Rings",
+	"six Geese-a-Laying",
+	"seven Swans-a-Swimming",
+	"eight Maids-a-Milking",
+	"nine Ladies Dancing",
+	"ten Lords-a-Leaping",
+	"eleven Pipers Piping",
+	"twelve Drummers Drumming",
+}
+
+func giftsForDay(day int) string {
+	switch day {
+	case 0, 1:
+		return gifts[day]
+	case 2:
+		return fmt.Sprintf(
+			"%s, and %s",
+			gifts[day],
+			gifts[day-1],
+		)
+	default:
+		return fmt.Sprintf(
+			"%s, %s",
+			gifts[day],
+			giftsForDay(day-1),
+		)
+	}
+}
+
+func Verse(day int) string {
+	return fmt.Sprintf(
+		"On the %s day of Christmas my true love gave to me: %s.",
+		ordinals[day],
+		giftsForDay(day),
+	)
+}
+
+func Song() (song string) {
+	for day := 1; day <= 12; day++ {
+		song += fmt.Sprintf("%s\n", Verse(day))
+	}
+	return
+}

go/twelve-days/twelve_days_test.go

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+package twelve
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+)
+
+type testCase struct {
+	input    int
+	expected string
+}
+
+var testCases = []testCase{
+	{1, "On the first day of Christmas my true love gave to me: a Partridge in a Pear Tree."},
+	{2, "On the second day of Christmas my true love gave to me: two Turtle Doves, and a Partridge in a Pear Tree."},
+	{3, "On the third day of Christmas my true love gave to me: three French Hens, two Turtle Doves, and a Partridge in a Pear Tree."},
+	{4, "On the fourth day of Christmas my true love gave to me: four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree."},
+	{5, "On the fifth day of Christmas my true love gave to me: five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree."},
+	{6, "On the sixth day of Christmas my true love gave to me: six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree."},
+	{7, "On the seventh day of Christmas my true love gave to me: seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree."},
+	{8, "On the eighth day of Christmas my true love gave to me: eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree."},
+	{9, "On the ninth day of Christmas my true love gave to me: nine Ladies Dancing, eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree."},
+	{10, "On the tenth day of Christmas my true love gave to me: ten Lords-a-Leaping, nine Ladies Dancing, eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree."},
+	{11, "On the eleventh day of Christmas my true love gave to me: eleven Pipers Piping, ten Lords-a-Leaping, nine Ladies Dancing, eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree."},
+	{12, "On the twelfth day of Christmas my true love gave to me: twelve Drummers Drumming, eleven Pipers Piping, ten Lords-a-Leaping, nine Ladies Dancing, eight Maids-a-Milking, seven Swans-a-Swimming, six Geese-a-Laying, five Gold Rings, four Calling Birds, three French Hens, two Turtle Doves, and a Partridge in a Pear Tree."},
+}
+
+// diff compares two multi-line strings and returns a helpful comment
+func diff(got, want string) string {
+	g := strings.Split(got, "\n")
+	w := strings.Split(want, "\n")
+	for i := 0; ; i++ {
+		switch {
+		case i < len(g) && i < len(w):
+			if g[i] == w[i] {
+				continue
+			}
+			return fmt.Sprintf("-- first difference in line %d:\n"+
+				"-- got : %q\n-- want: %q\n", i+1, g[i], w[i])
+		case i < len(g):
+			return fmt.Sprintf("-- got %d extra lines after line %d:\n"+
+				"-- first extra line: %q\n", len(g)-len(w), i, g[i])
+		case i < len(w):
+			return fmt.Sprintf("-- got %d correct lines, want %d more lines:\n"+
+				"-- want next: %q\n", i, len(w)-i, w[i])
+		default:
+			return "no differences found"
+		}
+	}
+}
+
+func TestSong(t *testing.T) {
+	var expected = ""
+	for _, test := range testCases {
+		expected += test.expected + "\n"
+	}
+	actual := Song()
+	if expected != actual {
+		t.Fatalf("Song() =\n%s\n  want:\n%s\n%s", actual, expected, diff(actual, expected))
+	}
+}
+
+func TestVerse(t *testing.T) {
+	for _, test := range testCases {
+		actual := Verse(test.input)
+		if actual != test.expected {
+			t.Errorf("Twelve Days test [%d], expected [%s], actual [%s]", test.input, test.expected, actual)
+		}
+	}
+}