refactor(tree): simplified SubTree implementation

internal/tree/treeconfig.go

@@ -128,21 +128,18 @@ func (t *Tree) PeersOf(nodeID hotstuff.ID) []hotstuff.ID {
 	return t.ChildrenOf(parent)
 }
 
-// SubTree returns all the nodes of its subtree.
+// SubTree returns all subtree nodes of this tree's replica.
 func (t *Tree) SubTree() []hotstuff.ID {
-	nodeID := t.id
-	subTreeNodes := make([]hotstuff.ID, 0)
-	children := t.ChildrenOfNode(nodeID)
-	queue := make([]hotstuff.ID, 0)
-	queue = append(queue, children...)
-	subTreeNodes = append(subTreeNodes, children...)
+	children := t.ChildrenOf(t.id)
 	if len(children) == 0 {
-		return subTreeNodes
+		return nil
 	}
+	subTreeNodes := slices.Clone(children)
+	queue := slices.Clone(children)
 	for len(queue) > 0 {
 		child := queue[0]
 		queue = queue[1:]
-		children := t.ChildrenOfNode(child)
+		children := t.ChildrenOf(child)
 		subTreeNodes = append(subTreeNodes, children...)
 		queue = append(queue, children...)
 	}

internal/tree/treeconfig_test.go

@@ -93,10 +93,10 @@ func TestTreeAPIWithInitializeWithPIDs(t *testing.T) {
 		if tree.TreeHeight() != test.height {
 			t.Errorf("Expected height %d, got %d", test.height, tree.TreeHeight())
 		}
-		gotChildren := tree.ChildrenOf()
+		gotChildren := tree.NodeChildren()
 		sort.Slice(gotChildren, func(i, j int) bool { return gotChildren[i] < gotChildren[j] })
 		if len(gotChildren) != len(test.children) || !slices.Equal(gotChildren, test.children) {
-			t.Errorf("Expected %v, got %v", test.children, tree.ChildrenOf())
+			t.Errorf("Expected %v, got %v", test.children, tree.NodeChildren())
 		}
 		subTree := tree.SubTree()
 		sort.Slice(subTree, func(i, j int) bool { return subTree[i] < subTree[j] })
@@ -112,8 +112,8 @@ func TestTreeAPIWithInitializeWithPIDs(t *testing.T) {
 		if tree.IsRoot(test.id) != test.isRoot {
 			t.Errorf("Expected %t, got %t", test.isRoot, tree.IsRoot(test.id))
 		}
-		if tree.GetHeight() != test.replicaHeight {
-			t.Errorf("Expected %d, got %d", test.replicaHeight, tree.GetHeight())
+		if tree.NodeHeight() != test.replicaHeight {
+			t.Errorf("Expected %d, got %d", test.replicaHeight, tree.NodeHeight())
 		}
 		gotPeers := tree.PeersOf(test.id)
 		sort.Slice(gotPeers, func(i, j int) bool { return gotPeers[i] < gotPeers[j] })
@@ -130,7 +130,7 @@ func benchmarkGetChildren(size int, bf int, b *testing.B) {
 	}
 	tree := CreateTree(1, bf, ids)
 	for i := 0; i < b.N; i++ {
-		tree.ChildrenOf()
+		tree.NodeChildren()
 	}
 }