      "\n",
      "* Can we assume we already have a Node class with an insert method?\n",
      "    * Yes"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
 
</s> remove     "* Space: O(m), where m is the recursion depth, or O(1) if using an iterative approach\n",
    "\n",
    "Note:\n",
    "* This is a form of a depth-first traversal"
 </s> add     "* Space: O(m), where m is the recursion depth, or O(1) if using an iterative approach" </s> remove     "## Problem: Implement depth-first searches (in-order, pre-order, post-order traversals) on a binary tree.\n",
 </s> add     "## Problem: Implement depth-first traversals (in-order, pre-order, post-order) on a binary tree.\n", </s> remove     "## Problem: Implement depth-first searches (in-order, pre-order, post-order traversals) on a binary tree.\n",
 </s> add     "## Problem: Implement depth-first traversals (in-order, pre-order, post-order) on a binary tree.\n", </s> remove     "Note:\n",
    "* This is a form of a depth-first traversal\n",
    "\n",
 </s> add 
    "    * Yes\n",
    "* What should we do with each node when we process it?\n",
    "    * Call an input method `visit_func` on the node\n",
    "* Can we assume this fits in memory?\n",
      "\n",
      "* Can we assume we already have a Node class with an insert method?\n",
    "    * Yes\n",
    "* What should we do with each node when we process it?\n",
    "    * Call an input method `visit_func` on the node\n",
    "* Can we assume this fits in memory?\n",
      "    * Yes"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
keep add keep keep keep keep keep keep
 Polish tree dfs challenge and solution (#78)

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