Add linear solution for day2 - no division.

.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 {

day3/problem.go

@@ -30,22 +30,24 @@ func Serialize(root *Node) string {
 	return strings.Join(serialized, " ")
 }
 
-func preorderDeserialize(serialized []string) *Node {
+func preorderDeserialize(serialized []string) (*Node, int) {
 	if len(serialized) == 0 || serialized[0] == "-1" {
-		return nil
+		return nil, 1
 	}
 	v, err := strconv.Atoi(serialized[0])
 	if err != nil {
 		panic("bad serialized data cannot be deserialized")
 	}
 	node := &Node{val: v}
-	node.left = preorderDeserialize(serialized[1:])
-	node.right = preorderDeserialize(serialized[2:])
-	return node
+	advanceLeft, advanceRight := 0, 0
+	node.left, advanceLeft = preorderDeserialize(serialized[1:])
+	node.right, advanceRight = preorderDeserialize(serialized[1+advanceLeft:])
+	return node, 1 + advanceLeft + advanceRight
 }
 
 // Deserialize converts a string into a general binary tree.
 func Deserialize(data string) *Node {
 	serialized := strings.Split(data, " ")
-	return preorderDeserialize(serialized)
+	result, _ := preorderDeserialize(serialized)
+	return result
 }

day3/problem_test.go

@@ -1,19 +1,41 @@
 package day3
 
 import (
-	//	"log"
 	"testing"
 )
 
 func TestSerializeAndDeserialize(t *testing.T) {
 	t.Parallel()
-	root := &Node{val: 20,
-		left: nil,
-		right: &Node{val: 8, left: nil,
-			right: &Node{val: 10, left: nil,
-				right: &Node{val: 5}}},
+	root := &Node{
+		val: 20,
+		left: &Node{
+			val: 5,
+			left: &Node{
+				val:  10,
+				left: nil,
+				right: &Node{
+				val:   5,
+					left:  nil,
+					right: nil,
+				},
+			},
+			right: nil,
+		},
+		right: &Node{
+			val:  8,
+			left: nil,
+			right: &Node{
+				val:  10,
+				left: nil,
+				right: &Node{
+					val:   5,
+					left:  nil,
+					right: nil,
+				},
+			},
+		},
 	}
-	expected := "20 -1 8 -1 10 -1 5 -1 -1"
+	expected := "20 5 10 -1 5 -1 -1 -1 8 -1 10 -1 5 -1 -1"
 	var result string
 	if result = Serialize(root); result != expected {
 		t.Errorf("Expected %v but got %v", expected, result)
@@ -49,21 +71,21 @@ func TreeEquality(t1, t2 *Node) bool {
 }
 
 // inorder is a method to debug your inorder traversal of the tree
-//func inorder(n *Node) {
-//if n == nil {
-//return
-//}
-//if n.left != nil {
-//log.Println("going left")
-//} else {
-//log.Println("nothing to the left")
-//}
-//inorder(n.left)
-//log.Println(n.val)
-//if n.right != nil {
-//log.Println("going right")
-//} else {
-//log.Println("nothing to the right")
-//}
-//inorder(n.right)
-//}
+// func inorder(n *Node) {
+// if n == nil {
+// return
+// }
+// if n.left != nil {
+// log.Println("going left")
+// } else {
+// log.Println("nothing to the left")
+// }
+// inorder(n.left)
+// log.Println(n.val)
+// if n.right != nil {
+// log.Println("going right")
+// } else {
+// log.Println("nothing to the right")
+// }
+// inorder(n.right)
+// }