二叉树的中序遍历

//go
//* Definition for a binary tree node.
type TreeNode struct {
 Val int
 Left *TreeNode
 Right *TreeNode
}

var res []int

func inorderTraversal(root *TreeNode) []int {
    res = make([]int, 0)
    inorder(root)
    return res
}

func inorder(root *TreeNode) {
    if root != nil {
        inorder(root.Left) 
        res = append(res, root.Val)
        inorder(root.Right)
    }
}

//go

type ColorNode struct {
 node *TreeNode
 color string
}

func inorderTraversal(root *TreeNode) []int {
 if root == nil {
  return []int{}
 }
 var res []int
 var stack []*ColorNode
 stack = append(stack, &ColorNode{root, "white"})
 var cn *ColorNode

 for len(stack) != 0 {
  cn = stack[len(stack)-1]
  stack = stack[:len(stack)-1] // 以上两句等同于 cn = stack.pop() ，别忘了加这句
  if cn.color == "white" {
   // 因为栈是先进后出，所以中序是 右-根-左 的顺序添加
   if cn.node.Right != nil {
    stack = append(stack, &ColorNode{cn.node.Right,"white"})
   }
   stack = append(stack,&ColorNode{cn.node, "gray"})
   if cn.node.Left != nil {
    stack = append(stack, &ColorNode{cn.node.Left, "white"})
   }
  }else {
   res = append(res, cn.node.Val)
  }
 }

 return res
}