Binary Tree Inorder Traversal-LeetCode#94

94. Binary Tree Inorder Traversal

Given a binary tree, return the inorder traversal of its nodes’ values.
Example:

Input: [1,null,2,3]
   1
    \
     2
    /
   3
Output: [1,3,2]

Follow up: Recursive solution is trivial, could you do it iteratively?
二叉树的中序遍历
递归做很简单

public class BinaryTreeInorderTraversal {
    public List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> res = new ArrayList<>();
        dfs(root, res);
        return res;
    }
    public void dfs(TreeNode root, List<Integer> res) {
        if (root == null) {
            return;
        }
        dfs(root.left, res);
        res.add(root.val);
        dfs(root.right, res);
    }
    public static void main(String[] args) {
        TreeNode root = new TreeNode(1);
        root.right = new TreeNode(2);
        root.right.left = new TreeNode(3);
        BinaryTreeInorderTraversal binaryTreeInorderTraversal = new BinaryTreeInorderTraversal();
        List<Integer> res = binaryTreeInorderTraversal.inorderTraversal(root);
        for (Integer i :
                res) {
            System.out.println(i);
        }
    }
}

题目提示是否能尝试用迭代做，