LeetCode-94 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?

 

要求使用非递归解法，代码如下：

public List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> list = new ArrayList<Integer>();
        if(root == null)
            return list;
        Stack<TreeNode> nodes = new Stack<TreeNode>(); 
        nodes.add(root);
        
        while(!nodes.isEmpty()) {
            while(nodes.peek().left != null) {
                nodes.add(nodes.peek().left);
            }
            TreeNode curr = nodes.pop();
            while(curr.right == null) {
                list.add(curr.val);
                if(nodes.isEmpty())
                    return list;
                curr = nodes.pop();
            }
            list.add(curr.val);
            nodes.push(curr.right);
        }
        return list;
    }