Create Binary Tree Inorder Traversal

二叉树的中序遍历。
Binary Tree Inorder Traversal Total Accepted: 24736 Total Submissions: 69681 My Submissions
Given a binary tree, return the inorder traversal of its nodes' values.

For example:
Given binary tree {1,#,2,3},
   1
    \
     2
    /
   3
return [1,3,2].

Note: Recursive solution is trivial, could you do it iteratively?