Add Go codes to docs, including

the chapter of stack and queue, the chapter of tree.

codes/go/chapter_tree/binary_tree_dfs.go

@@ -8,56 +8,37 @@ import (
 	. "github.com/krahets/hello-algo/pkg"
 )
 
-// preOrder 前序遍历
-func preOrder(root *TreeNode) (nums []int) {
-	var preOrderHelper func(node *TreeNode)
-	// 匿名函数
-	preOrderHelper = func(node *TreeNode) {
-		if node == nil {
-			return
-		}
-		// 访问优先级：根结点 -> 左子树 -> 右子树
-		nums = append(nums, node.Val)
-		preOrderHelper(node.Left)
-		preOrderHelper(node.Right)
+var nums []int
+
+/* 前序遍历 */
+func preOrder(node *TreeNode) {
+	if node == nil {
+		return
 	}
-	// 函数调用
-	preOrderHelper(root)
-	return
+	// 访问优先级：根结点 -> 左子树 -> 右子树
+	nums = append(nums, node.Val)
+	preOrder(node.Left)
+	preOrder(node.Right)
 }
 
-// inOrder 中序遍历
-func inOrder(root *TreeNode) (nums []int) {
-	var inOrderHelper func(node *TreeNode)
-	// 匿名函数
-	inOrderHelper = func(node *TreeNode) {
-		if node == nil {
-			return
-		}
-		// 访问优先级：左子树 -> 根结点 -> 右子树
-		inOrderHelper(node.Left)
-		nums = append(nums, node.Val)
-		inOrderHelper(node.Right)
+/* 中序遍历 */
+func inOrder(node *TreeNode) {
+	if node == nil {
+		return
 	}
-	// 函数调用
-	inOrderHelper(root)
-	return
+	// 访问优先级：左子树 -> 根结点 -> 右子树
+	inOrder(node.Left)
+	nums = append(nums, node.Val)
+	inOrder(node.Right)
 }
 
-// postOrder 后序遍历
-func postOrder(root *TreeNode) (nums []int) {
-	var postOrderHelper func(node *TreeNode)
-	// 匿名函数
-	postOrderHelper = func(node *TreeNode) {
-		if node == nil {
-			return
-		}
-		// 访问优先级：左子树 -> 右子树 -> 根结点
-		postOrderHelper(node.Left)
-		postOrderHelper(node.Right)
-		nums = append(nums, node.Val)
+/* 后序遍历 */
+func postOrder(node *TreeNode) {
+	if node == nil {
+		return
 	}
-	// 函数调用
-	postOrderHelper(root)
-	return
+	// 访问优先级：左子树 -> 右子树 -> 根结点
+	postOrder(node.Left)
+	postOrder(node.Right)
+	nums = append(nums, node.Val)
 }