Clojure Quicksort and More!

clojure_quicksort.cjl

//Mark Holmberg [email protected]
//CS350, Programming Languages
//date: Mon Sep 12 09:33:11 MDT 2011
//Clojure

//http://en.wikipedia.org/wiki/Quicksort
((fn [x] (* x x)) 5)

//calling a function with only one parameter
#(* % %)

//square all the elements in a list

//as a vector
(map #(* % %) [1 2 3 4 5])

//as a list
(map #(* % %) '(1 2 3 4 5))


//how to define our own map function called 'MyMap'
(defn mymap [f lst] (if (empty? lst) nil (cons (f (first lst)) (mymap f(rest lst)))))

//the test
(mymap #(* % %) '(1 2 3 4 5))

//filter
(filter nil? '(1 2 nil 3 4))

//grab everything that isn't nil
(filter #(not (nil? %)) '(1 2 nil 3 4))

(defn myfilter [f lst]
        (if (empty? lst)
		lst
		(if (f (first lst))
		(cons (first lst) (myfilter f(rest lst)))
		(myfilter f(rest lst)))))

//the test
(myfilter #(not (nil? %)) '(1 2 nil 3 4))

//A quicksort function
(defn mypartition [pivot lst]
(list (filter #(<= % pivot) lst)
(filter #(> % pivot) lst)))


(defn append [a b]
(if (empty? a)
b
(cons (first a) (append (rest a) b))))


//a good start but not finished
(defn quicksort [lst]
(if (< (count lst) 2)
lst
(let [pivot (first lst)
[less greater] (mypartition pivot (rest lst))]
(append (quicksort less)
(cons pivot (quicksort greater))))))