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janet/examples/3sum.janet
Calvin Rose eae4e0dede Add functionality that allows the set macro to
take a tuple as an l-value. Remove the old
multi-sym report in anticipation of a different
mechanism.
2019-01-06 19:33:27 -05:00

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(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 (s k) k))
(for i 0 len
(for j 0 len
(def k (get tab (- 0 (s i) (s j))))
(when (and k (not= k i) (not= k j) (not= i j))
(put solutions {i true j true k true} true))))
(map keys (keys solutions)))
(def arr @[2 4 1 3 8 7 -3 -1 12 -5 -8])
(print "3sum of " (string/pretty arr) ":")
(print (string/pretty (sum3 arr)))