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sw-samuraj/blog-catalan.clj

Last active March 18, 2017 16:09
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Counts a Catalan number through a binomial coefficient.
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blog-catalan.clj
(defn factorial [n]
"Counts a factorial."
(reduce *' (range 1 (inc n))))
(defn binomial [n k]
"Counts a binomial coefficient."
(/ (factorial n)
(*' (factorial k)
(factorial (- n k)))))
(defn catalan [n]
"Counts a Catalan number."
(* (/ 1 (inc n))
(binomial (* 2 n) n)))
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