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djtrack16/rankofPerm.clj

Created January 13, 2015 02:18
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given a string and rank, find the permutation is at that index of the sorted permutations
Raw
rankofPerm.clj
(fn [s rank]
(let [n (count s) step (reduce * (range 1 n))]
(loop [i 0 s (sort s) acc '() r rank step step]
(let [index (quot r step)]
(if (= 1 (count s))
(clojure.string/join (concat acc s))
(recur (inc i)
(concat (take index s) (drop (inc index) s))
(concat acc [(nth s index)])
(- r (* index step))
(quot step (- n (inc i)))))))))
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