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Dijkstra's algorithm in Clojure
; 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))
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