Balanced Binary Tree

pullrequests/balanced_binary_tree/step1.go

@@ -0,0 +1,34 @@
+//lint:file-ignore U1000 Ignore all unused code
+package template
+
+import "math"
+
+type TreeNode struct {
+	Val   int
+	Left  *TreeNode
+	Right *TreeNode
+}
+
+/*
+時間：12分
+
+左右の木の高さを比べてバランスしているかを確かめるのと、そもそもその部分木自体がバランスしているのかも確かめる必要があるので、別途再帰用の補助関数を作ることにした。
+*/
+type Balance struct {
+	isBalanced bool
+	height     int
+}
+
+func isBalancedStep1(root *TreeNode) bool {
+	return isHeightBalanced(root).isBalanced
+}
+
+func isHeightBalanced(root *TreeNode) *Balance {
+	if root == nil {
+		return &Balance{true, 0}
+	}
+	leftBalance := isHeightBalanced(root.Left)
+	rightBalance := isHeightBalanced(root.Right)
+	isBalanced := leftBalance.isBalanced && rightBalance.isBalanced && (math.Abs(float64(leftBalance.height-rightBalance.height)) <= 1.0)
+	return &Balance{isBalanced, max(leftBalance.height, rightBalance.height) + 1}
+}

pullrequests/balanced_binary_tree/step2.go

@@ -0,0 +1,30 @@
+//lint:file-ignore U1000 Ignore all unused code
+package template
+
+import "math"
+
+/*
+読みやすくなるようにリファクタした。
+Go的にはleftBalance.isBalancedのように同じ名前が繰り返されるのを嫌う（Go styleguideにも書いてある）ので、繰り返さないように直したりした。
+
+正直、TreeBalanceやcheckBalanceという関数名はしっくりきていないけど、より良い名前が思いつかなかった。
+*/
+type TreeBalance struct {
+	isBalanced bool
+	height     int
+}
+
+func isBalancedStep2(root *TreeNode) bool {
+	return checkBalanceStep2(root).isBalanced
+}
+
+func checkBalanceStep2(root *TreeNode) *TreeBalance {
+	if root == nil {
+		return &TreeBalance{true, 0}
+	}
+	left, right := checkBalanceStep2(root.Left), checkBalanceStep2(root.Right)
+	isBalanced := left.isBalanced && right.isBalanced &&
+		math.Abs(float64(left.height-right.height)) <= 1.0
+	height := max(left.height, right.height) + 1
+	return &TreeBalance{isBalanced, height}
+}

pullrequests/balanced_binary_tree/step3.go

@@ -0,0 +1,31 @@
+//lint:file-ignore U1000 Ignore all unused code
+package template
+
+import "math"
+
+/*
+Go styleguideを見ると、下記のように書かれているのでポインタではなく、直接構造体を渡すように直した。
+
+> Do not pass pointers as function arguments just to save a few bytes. If a function reads its argument x only as *x throughout, then the argument shouldn’t be a pointer. Common instances of this include passing a pointer to a string (*string) or a pointer to an interface value (*io.Reader). In both cases, the value itself is a fixed size and can be passed directly.
+>
+> This advice does not apply to large structs, or even small structs that may increase in size. In particular, protocol buffer messages should generally be handled by pointer rather than by value. The pointer type satisfies the proto.Message interface (accepted by proto.Marshal, protocmp.Transform, etc.), and protocol buffer messages can be quite large and often grow larger over time.
+*/
+type treeBalance struct {
+	isBalanced bool
+	height     int
+}
+
+func isBalancedStep3(root *TreeNode) bool {
+	return checkBalanceStep3(root).isBalanced
+}
+
+func checkBalanceStep3(root *TreeNode) treeBalance {
+	if root == nil {
+		return treeBalance{true, 0}
+	}
+	left, right := checkBalanceStep3(root.Left), checkBalanceStep3(root.Right)
+	isBalanced := left.isBalanced && right.isBalanced &&
+		math.Abs(float64(left.height-right.height)) <= 1.0
+	height := max(left.height, right.height) + 1
+	return treeBalance{isBalanced, height}
+}