namespace _94._Binary_Tree_Inorder_Traversal;

public class Solution
{
    public List<int> inorderTraversal(TreeNode root)
    {
        List<int> res = new List<int>();
        Stack<TreeNode> stack = new Stack<TreeNode>();
        TreeNode? curr = root;
        while (curr != null || stack.Count > 0)
        {
            while (curr != null)
            {
                stack.Push(curr);
                curr = curr.left;
            }
            curr = stack.Pop();
            res.Add(curr.val);
            curr = curr.right!;
        }
        return res;
    }
}