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janet/examples/3sum.dst
2018-05-05 14:41:47 -04:00

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(import "examples/iterators.dst")
(defn sum3
"Solve the 3SUM problem in O(n^2) time."
[s]
(def tab @{})
(def solutions @{})
(def len (length s))
(for [k 0 len]
(put tab (get s k) k))
(for [i 0 len]
(for [j 0 len]
(def k (get tab (- 0 (get s i) (get s j))))
(when (and k (not= k i) (not= k j) (not= i j))
(put solutions {i true j true k true} true))))
(iter2array (map (fn [x] (iter2array (keys x))) (keys solutions))))