     "metadata": {},
     "source": [
      "## Solution Notebook\n",
      "\n",
      "Review the [solution notebook](https://github.com/donnemartin/interactive-coding-challenges/graphs_trees/tree_dfs/dfs_solution.ipynb) for a discussion on algorithms and code solutions."
     ]
    },
    {
     "cell_type": "code",
     "execution_count": null,
 
</s> remove     "Refer to the [solution notebook](https://github.com/donnemartin/interactive-coding-challenges/graphs_trees/tree_dfs/dfs_solution.ipynb).  If you are stuck and need a hint, the solution notebook's algorithm discussion might be a good place to start."
 </s> add     "Refer to the [Solution Notebook](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/tree_dfs/dfs_solution.ipynb).  If you are stuck and need a hint, the solution notebook's algorithm discussion might be a good place to start." </s> remove   },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": []
 </s> add 
    "Review the [Solution Notebook](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/tree_dfs/dfs_solution.ipynb) for a discussion on algorithms and code solutions."
     "metadata": {},
     "source": [
      "## Solution Notebook\n",
      "\n",
    "Review the [Solution Notebook](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/tree_dfs/dfs_solution.ipynb) for a discussion on algorithms and code solutions."
     ]
    },
    {
     "cell_type": "code",
     "execution_count": null,
keep keep keep keep replace keep keep keep keep keep
 Updated solution notebook nbviewer link. 
graphs_trees/tree_dfs/dfs_challenge.ipynb