dijkstra.clj

; http://www.algolist.com/Dijkstra's_algorithm

(defn dijkstra [g src]
  (loop [dsts (assoc (zipmap (keys g) (repeat nil)) src 0)
         curr src
         unvi (apply hash-set (keys g))]
    (if (empty? unvi)
      dsts
      (let [unvi  (disj unvi curr)
            nextn (first (sort-by #(% dsts) unvi))
            nrds  (zipmap (keys g) (map #(select-keys % unvi) (vals g)))]
        (if (empty? (curr nrds))
          (recur dsts nextn unvi)
          (let [cdst  (curr dsts)
                roads (select-keys (curr g) unvi)
                reslt (zipmap (keys dsts)
                        (map #(if-let [rd (% roads)]
                                (let [idst (% dsts)
                                      sum  (+ cdst (% roads))]
                                  (if (or (nil? idst)
                                          (< sum idst))
                                    sum idst))
                                (% dsts)) (keys dsts)))]
            (recur reslt nextn unvi)))))))

; ---

(def demo-graph {:red    {:green 10, :blue   5, :orange 8},
                 :green  {:red 10,   :blue   3},
                 :blue   {:green 3,  :red    5, :purple 7},
                 :purple {:blue 7,   :orange 2},
                 :orange {:purple 2, :red    2}})

(prn (dijkstra demo-graph :red))