Add arrays package

arrays/sum.go

@@ -7,3 +7,17 @@ func Sum(numbers []int) int {
 	}
 	return sum
 }
+
+func SumAllTails(numbersToSum ...[]int) []int {
+	sums := make([]int, 0, len(numbersToSum))
+
+	for _, numbers := range numbersToSum {
+		if len(numbers) == 0 {
+			sums = append(sums, 0)
+		} else {
+			tail := numbers[1:]
+			sums = append(sums, Sum(tail))
+		}
+	}
+	return sums
+}

arrays/sum_test.go

@@ -1,6 +1,9 @@
 package main
 
-import "testing"
+import (
+	"reflect"
+	"testing"
+)
 
 func TestSum(t *testing.T) {
 
@@ -27,3 +30,33 @@ func TestSum(t *testing.T) {
 	})
 
 }
+
+//func TestSumAll(t *testing.T) {
+//got := SumAll([]int{1, 2}, []int{0, 9})
+//want := []int{3, 9}
+
+//if !reflect.DeepEqual(got, want) {
+//t.Errorf("got %v want %v", got, want)
+//}
+//}
+
+func TestSumAllTails(t *testing.T) {
+	checkSums := func(t testing.TB, got, want []int) {
+		t.Helper()
+		if !reflect.DeepEqual(got, want) {
+			t.Errorf("got %v want %v", got, want)
+		}
+	}
+
+	t.Run("make the sums of tails of", func(t *testing.T) {
+		got := SumAllTails([]int{1, 2}, []int{0, 9})
+		want := []int{2, 9}
+		checkSums(t, got, want)
+	})
+
+	t.Run("safely sum empty slices", func(t *testing.T) {
+		got := SumAllTails([]int{}, []int{3, 4, 5})
+		want := []int{0, 9}
+		checkSums(t, got, want)
+	})
+}