[Lintcode] 67. Binary Tree Inorder Traversal

給出一棵二叉樹，返回其中序遍歷。

public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: Inorder in ArrayList which contains node values.
     */
    public List<Integer> inorderTraversal(TreeNode root) {
        Stack<TreeNode> stack = new Stack<TreeNode>();
        List<Integer> result = new ArrayList<Integer>();
        
        TreeNode curt = root;
        
        while (curt != null || !stack.empty()) {
            while (curt != null) {
                stack.add(curt);
                curt = curt.left;
            }
            curt = stack.pop();
            result.add(curt.val);
            curt = curt.right;
        }
        
        return result;
    }
}