From eeef9622dfd2db6ed7480a512e870f733ce747ed Mon Sep 17 00:00:00 2001
From: Drew Bednar <drew@runcible.io>
Date: Thu, 7 Mar 2024 11:16:57 -0500
Subject: [PATCH] Finished up arrays and slice lesson

---
 learn_go_with_tests/arrays/go.mod      |  2 +-
 learn_go_with_tests/arrays/sum.go      | 36 +++++++++++++++++++++++++-
 learn_go_with_tests/arrays/sum_test.go | 26 +++++++++++++++++++
 3 files changed, 62 insertions(+), 2 deletions(-)

diff --git a/learn_go_with_tests/arrays/go.mod b/learn_go_with_tests/arrays/go.mod
index 88bf4e7..fcc2e9c 100644
--- a/learn_go_with_tests/arrays/go.mod
+++ b/learn_go_with_tests/arrays/go.mod
@@ -1,3 +1,3 @@
-module myarray
+module arrays
 
 go 1.21.0
diff --git a/learn_go_with_tests/arrays/sum.go b/learn_go_with_tests/arrays/sum.go
index 2bd2ec5..94ccccf 100644
--- a/learn_go_with_tests/arrays/sum.go
+++ b/learn_go_with_tests/arrays/sum.go
@@ -27,5 +27,39 @@ func Sum(a []int) int {
 
 // SumAll
 func SumAll(numbersToSum ...[]int) []int {
-	return nil
+	// lengthOfNumbers := len(numbersToSum)
+
+	//There's a new way to create a slice. make allows you to create a slice with a starting capacity of the len of the numbersToSum we need to work through.
+	// sums := make([]int, lengthOfNumbers)
+
+	// for i, numbers := range numbersToSum {
+	// 	sums[i] = Sum(numbers)
+	// }
+
+	// Using the append method you do not have to worry about capacity and index errors
+	// append will create a new slice with greater capacity and the new value added to it.
+	// The is a different between len() and capacity() capacity is the allocated size, and there
+	// is an algorithm used by append to determine when it needs to change.
+	var sums []int
+
+	for _, numbers := range numbersToSum {
+		sums = append(sums, Sum(numbers))
+	}
+
+	return sums
+}
+
+func SumAllTails(numbersToSum ...[]int) []int {
+	var sums []int
+
+	for _, numbers := range numbersToSum {
+		if len(numbers) == 0 {
+			sums = append(sums, 0)
+		} else {
+			tails := numbers[1:]
+			sums = append(sums, Sum(tails))
+		}
+	}
+
+	return sums
 }
diff --git a/learn_go_with_tests/arrays/sum_test.go b/learn_go_with_tests/arrays/sum_test.go
index 3ead916..1c275e0 100644
--- a/learn_go_with_tests/arrays/sum_test.go
+++ b/learn_go_with_tests/arrays/sum_test.go
@@ -81,3 +81,29 @@ func TestSumAll(t *testing.T) {
 		t.Errorf("Using slices.Equal got %v expected %v given", got, expected)
 	}
 }
+
+// The tail of a collection is all items in the collection except the first one (the "head").
+func TestSumAllTails(t *testing.T) {
+
+	// Another example of helper function
+	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("test slices of same lenght", func(t *testing.T) {
+		got := SumAllTails([]int{1, 2}, []int{0, 9})
+		want := []int{2, 9}
+
+		checkSums(t, got, want)
+	})
+
+	t.Run("test an empty slice and slice of different len", func(t *testing.T) {
+		got := SumAllTails([]int{}, []int{0, 4, 5})
+		want := []int{0, 9}
+
+		checkSums(t, got, want)
+	})
+}