How to create a binary tree use struct in golang? - go

Question

I want to create a binary tree and initialize the tree use golang.
And the codes like these:
package Tree
import "fmt"
type TreeNode struct {
Left *TreeNode
Right *TreeNode
Value int
}
func InsertNodeToTree(tree *TreeNode, node *TreeNode)(){
if tree == nil {
tree = node
}
if node.Value > tree.Value {
InsertNodeToTree(tree.Right, node)
}
if node.Value < tree.Value {
InsertNodeToTree(tree.Left, node)
}
}
func InitTree(values ...int) (root *TreeNode) {
rootNode := TreeNode{Value: values[0]}
for _, value := range values {
node := TreeNode{Value:value}
InsertNodeToTree(&rootNode, &node)
}
return &rootNode
}
func main() {
treeNode := InitTree(5, 4, 6, 8, 9, 7, 1, 3, 2)
fmt.Println(treeNode)
}
Why the tree's left and right are nil?
I pass the reference of the tree node, why not work?

Answer 1

In C/C++ programming language, you can use TreeNode *&tree.
But in golang programming language, you can not use *&.
tree is just a copy of the pointer, so you can't point the value to another TreeNode.
I modified your program, and it can run successfully now.
Maybe these codes you need:
package Tree
type TreeNode struct {
Left *TreeNode
Right *TreeNode
Value int
}
var DefaultValue int = -1024
func InsertNodeToTree(tree *TreeNode, node *TreeNode)(){
if tree == nil {
return
}
if tree.Value == DefaultValue {
tree.Value = node.Value
return
}
if node.Value > tree.Value {
if tree.Right == nil {
tree.Right = &TreeNode{Value: DefaultValue}
}
InsertNodeToTree(tree.Right, node)
}
if node.Value < tree.Value {
if tree.Left == nil {
tree.Left = &TreeNode{Value: DefaultValue}
}
InsertNodeToTree(tree.Left, node)
}
}
func InitTree(values ...int) (root *TreeNode) {
rootNode := TreeNode{Value: DefaultValue, Right: nil, Left: nil}
for _, value := range values {
node := TreeNode{Value:value}
InsertNodeToTree(&rootNode, &node)
}
return &rootNode
}

Answer 2

tree is only a copy of the pointer. Assigning to the variable is useless. Instead, you need to assign to an already existing node. For example:
https://play.golang.org/p/Agzby-Yinq
func InsertNodeToTree(tree *TreeNode, node *TreeNode) {
if tree == nil {
panic("cannot insert into nil root")
}
if node.Value > tree.Value {
if tree.Right == nil {
tree.Right = node
} else {
InsertNodeToTree(tree.Right, node)
}
}
if node.Value < tree.Value {
if tree.Left == nil {
tree.Left = node
} else {
InsertNodeToTree(tree.Left, node)
}
}
}