二叉树的中序遍历（非递归）

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def inorderTraversal(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        if root ==None:
            return []
        stack=[]
        result=[]
        while (len(stack)!=0 or  root!=None):
            while root!=None:
                stack.append(root)
                root =root.left
            if len(stack)!=0:
                root=stack.pop()
                result.append(root.val)
                root =root.right
        return result