sum: add SumAllTails

sum/sum.go

@@ -18,3 +18,17 @@ func SumAll(numbersToSum ...[]int) []int {
 
 	return res
 }
+
+func SumAllTails(numbersToSum ...[]int) []int {
+	res := make([]int, len(numbersToSum))
+
+	for i, numbers := range numbersToSum {
+		if len(numbers) == 0 {
+			res[i] = 0
+			continue
+		}
+		res[i] = Sum(numbers[1:])
+	}
+
+	return res
+}

sum/sum_test.go

@@ -26,3 +26,23 @@ func TestSumAll(t *testing.T) {
 		t.Errorf("got %d, expected %d", got, exp)
 	}
 }
+
+func TestSumAllTails(t *testing.T) {
+	t.Run("make the sums of some slices", func(t *testing.T) {
+		got := SumAllTails([]int{1, 2}, []int{0, 9})
+		exp := []int{2, 9}
+
+		if !slices.Equal(got, exp) {
+			t.Errorf("got %d, expected %d", got, exp)
+		}
+	})
+
+	t.Run("safely sum empty slices", func(t *testing.T) {
+		got := SumAllTails([]int{}, []int{3, 4, 5})
+		exp := []int{0, 9}
+
+		if !slices.Equal(got, exp) {
+			t.Errorf("got %d, expected %d", got, exp)
+		}
+	})
+}