94. Binary Tree Inorder Traversal

morris traversal 

using stack 
# 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 []
        res=[]
        stack=[]
        curr=root
        stack.append(curr)
        while stack:
            #loop and put all the left node in the stack, until there is no more left node 
            while curr and curr.left:
                stack.append(curr.left)
                curr=curr.left
            #pop the left most node , and add to result 
            curr=stack.pop()
            res.append(curr.val)
            #traverse the right node 
            curr=curr.right
            if curr:stack.append(curr)
        return res