    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "## Problem: Implement depth-first searches (in-order, pre-order, post-order traversals) on a binary tree.\n",
      "\n",
      "* [Constraints](#Constraints)\n",
      "* [Test Cases](#Test-Cases)\n",
      "* [Algorithm](#Algorithm)\n",
      "* [Code](#Code)\n",
 
</s>
    "## Problem: Implement depth-first traversals (in-order, pre-order, post-order) on a binary tree.\n",
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
    "## Problem: Implement depth-first traversals (in-order, pre-order, post-order) on a binary tree.\n",
      "\n",
      "* [Constraints](#Constraints)\n",
      "* [Test Cases](#Test-Cases)\n",
      "* [Algorithm](#Algorithm)\n",
      "* [Code](#Code)\n",
keep keep keep keep replace keep keep keep keep keep
 Polish tree dfs challenge and solution (#78)

Update constraints and algorithm discussion.
graphs_trees/tree_dfs/dfs_solution.ipynb