非递归遍历二叉树

#先序遍历
class Solution:
    def inorderTraversal(self, root: TreeNode) -> List[int]:
        stack,res = [root],[]
        while(stack):
            h = stack.pop()
               if h == None:continue
            if isinstance(h,TreeNode):
                stack += [h.right,h.left,h.val]
            else:
                res.append(h)

#中序遍历
class Solution:
    def inorderTraversal(self, root: TreeNode) -> List[int]:
        stack,res = [root],[]
        while(stack):
            h = stack.pop()
            if h == None:continue
            if isinstance(h,TreeNode):
                stack += [h.right,h.val,h.left]
            else:
                res.append(h)
        return res

#后序遍历
class Solution:
    def inorderTraversal(self, root: TreeNode) -> List[int]:
        stack,res = [root],[]
        while(stack):
            h = stack.pop()
            if h == None:continue
            if isinstance(h,TreeNode):
                stack += [h.val,h.right,h.left]
            else:
        return res