Merge ea0fb1f into 36687a4

.gitignore

@@ -10,3 +10,5 @@
 
 # Output of the go coverage tool, specifically when used with LiteIDE
 *.out
+go.mod
+.idea

day2/problem.go

@@ -16,6 +16,25 @@ func ProductsExceptI(arr []int) []int {
 	return result
 }
 
+// ProductsExceptINoDivisionLinear returns an array with the products of all numbers
+// except the value at the i-th position. Without using division.
+// O(N) time complexity.
+// O(1) space complexity.
+func ProductsExceptINoDivisionLinear(arr []int) []int {
+	result := make([]int, len(arr))
+	total := 1
+	for i := 0; i < len(arr); i++ {
+		result[i] = total
+		total *= arr[i]
+	}
+	total = 1
+	for i := len(arr) - 1; i >= 0; i-- {
+		result[i] *= total
+		total *= arr[i]
+	}
+	return result
+}
+
 // ProductsExceptINoDivision returns an array with the products of all numbers
 // except the value at the i-th position. Without using division.
 // O(N^2) time complexity.

day2/problem_test.go

@@ -21,6 +21,14 @@ func TestProductsExceptI(t *testing.T) {
 			}
 		}
 	})
+	t.Run("ProductsExceptINoDivisionLinear", func(t *testing.T) {
+		t.Parallel()
+		for _, tc := range testcases {
+			if result := ProductsExceptINoDivisionLinear(tc.input); !reflect.DeepEqual(result, tc.expected) {
+				t.Error("didn't get what I expected")
+			}
+		}
+	})
 	t.Run("ProductsExceptINoDivision", func(t *testing.T) {
 		t.Parallel()
 		for _, tc := range testcases {
@@ -39,6 +47,13 @@ func BenchmarkProductsExceptI(b *testing.B) {
 			}
 		}
 	})
+	b.Run("ProductsExceptINoDivisionLinear", func(b *testing.B) {
+		for i := 0; i < b.N; i++ {
+			for _, tc := range testcases {
+				ProductsExceptINoDivisionLinear(tc.input)
+			}
+		}
+	})
 	b.Run("ProductsExceptINoDivision", func(b *testing.B) {
 		for i := 0; i < b.N; i++ {
 			for _, tc := range testcases {