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amalloy/gist:8fdfdda5160581245f23 Secret

Last active August 29, 2015 14:13
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gistfile1.clj
(fn parens [n]
(set
(map (partial apply str)
((fn lazy-recur [open close]
(lazy-seq
(concat (when (pos? open)
(map #(cons \( %)
(lazy-recur (dec open) (inc close))))
(when (pos? close)
(map #(cons \) %)
(lazy-recur open (dec close))))
(when (= [0 0] [open close])
[""]))))
n 0))))
;; and much prettier with flatland.useful.seq/lazy-loop, of course:
(fn parens [n]
(set
(map (partial apply str)
(lazy-loop [open n, close 0]
(concat (when (pos? open)
(map #(cons \( %)
(lazy-recur (dec open) (inc close))))
(when (pos? close)
(map #(cons \) %)
(lazy-recur open (dec close))))
(when (= [0 0] [open close])
[""]))))))
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