;; I feel like this should be less lines
(defn add-edge
      [graph edge]
      (let [parts (clojure.string/split edge #",")
            from (first parts)
            to (second parts)
            graph (if (not (contains? graph from))
                    (assoc-in graph [from] #{})
                    graph)
            graph (if (not (contains? graph to))
                    (assoc-in graph [to] #{})
                    graph)]
           (update-in graph [from] conj to)))