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@acj
Created Oct 3, 2011
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Merge sort in Clojure
; Example usage: (mergesort [5 1 8 16 25 11 4])
(ns mergesort
(:use clojure.contrib.math))
(defn merge-two
"Merge two (already sorted) vectors"
[vec1 vec2]
(let [v1f (first vec1) v2f (first vec2)]
(cond
(empty? vec1) vec2
(empty? vec2) vec1
(< v1f v2f)
(cons v1f (merge-two (rest vec1) vec2))
:else
(cons v2f (merge-two (rest vec2) vec1)))))
(defn mergesort
"Sort a vector of numbers using the merge sort algorithm"
[vec]
(let [vecsize (count vec) seam (ceil (/ vecsize 2))]
(cond
(= vecsize 1) (vector (get vec 0))
(= vecsize 2)
(do
(if (< (get vec 0) (get vec 1))
(vector (get vec 0) (get vec 1))
(vector (get vec 1) (get vec 0))))
:else
(merge-two
(mergesort (subvec vec 0 seam))
(mergesort (subvec vec seam))))))
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