From: Ramakrishnan Muthukrishnan Date: Tue, 7 Sep 2010 10:55:25 +0000 (+0530) Subject: added the text examples in the section on unordered and ordered Sets X-Git-Url: https://git.rkrishnan.org/vdrive/%5B/%5D%20/uri/frontends/$top_link?a=commitdiff_plain;h=e53ed7581f1a251ceb579954e5a1075b276d38b8;p=sicp.git added the text examples in the section on unordered and ordered Sets --- diff --git a/src/sicp/ch2_3.clj b/src/sicp/ch2_3.clj index b1eea97..548d3aa 100644 --- a/src/sicp/ch2_3.clj +++ b/src/sicp/ch2_3.clj @@ -1,5 +1,6 @@ (ns sicp.ch2_3 - (:use [sicp.utils :only (error)])) + (:use [sicp.utils :only (error)] + [sicp.ex2_54 :only (equal?)])) (defn memq [item x] (cond @@ -65,3 +66,41 @@ (defn multiplicand [p] (second (rest p))) +;;;; 2.3.3 sets +(defn element-of-set? [x set] + (cond (empty? set) false + (equal? x (first set)) true + :else (element-of-set? x (rest set)))) + +;; add an element to the set, if not already part of the set and return the set. If +;; already part of the set, then return the set +(defn adjoin-set [x set] + (if (element-of-set? x set) + set + (cons x set))) + +;; intersection of two sets (i.e. elements of the set which are present in both the +;; sets) +(defn intersection-set [set1 set2] + (cond (or (empty? set1) (empty? set2)) () + (element-of-set? (first set1) set2) (cons (first set1) + (intersection-set (rest set1) set2)) + :else (intersection-set (rest set1) set2))) + + +;;; sets as ordered list +(defn element-of-set? [x set] + (cond (empty? set) false + (= (first set) x) true + (< x (first set)) false + :else (element-of-set? x (rest set)))) + +(defn intersection-set [set1 set2] + (if (or (empty? set1) (empty? set2)) + () + (let [x1 (first set1) + x2 (first set2)] + (cond (= x1 x2) (cons x1 (intersection-set (rest set1) + (rest set2))) + (< x1 x2) (intersection-set (rest set1) set2) + (< x2 x1) (intersection-set (rest set2) set1)))))