94. Binary Tree Inorder Traversal

# 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]
        """
        res=[]
        stack=[]
        cur=root
        while stack or cur:
            #add all possible left node into the stack 
            while cur:
                stack.append(cur)
                cur=cur.left
            #start adding to result from the left most node 
            cur=stack.pop()
            res.append(cur.val)
            #after reading the root node, start reading the right subtree 
            cur=cur.right
        return res