7.二叉树遍历递归版本

前序

type treenode struct {
	Val   int
	Left  *treenode
	Right *treenode
}

func (this *treenode) preOrder() {
	if this == nil {
		return
	}
	fmt.Println(this.Val)
	this.Left.preOrder()
	this.Right.preOrder()
}

中序

func (this *treenode) inOrder() {
	if this == nil {
		return
	}
	this.Left.inOrder()
	fmt.Println(this.Val)
	this.Right.inOrder()
}

后序 

func (this *treenode) TreeNode() {
	if this == nil {
		return
	}
	this.Left.TreeNode()
	this.Right.TreeNode()
	fmt.Println(this.Val)
}