leetcode94 Binary Tree Inorder Traversal

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?

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<int> inorderTraversal(TreeNode* root) {
        vector<int> ans;
        if(!root)
            return ans;
        stack<TreeNode*> st;
        TreeNode *rt=root;//现在要考虑的节点
        while(rt||!st.empty())
        {
            while(rt)
            {
                st.push(rt);
                rt=rt->left;
            }
            TreeNode *temp=st.top();
            st.pop();
            ans.push_back(temp->val);
            rt=temp->right;
        }
        return ans;
    }
};