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authorBen Sima <ben@bsima.me>2019-03-23 23:58:26 -0700
committerBen Sima <ben@bsima.me>2019-03-23 23:58:26 -0700
commitf50cecf2cb77cc073cb86a6016468a09d1c49fb0 (patch)
tree1ca9eda0a93a2e04e2dc44df8fc5113375a72c3d /lore/sicp/set.scm
parent5d4e34f146a358041099299d2f86a546eed25dea (diff)
Add semi-working bs
Diffstat (limited to 'lore/sicp/set.scm')
-rw-r--r--lore/sicp/set.scm42
1 files changed, 42 insertions, 0 deletions
diff --git a/lore/sicp/set.scm b/lore/sicp/set.scm
new file mode 100644
index 0000000..3d60c5c
--- /dev/null
+++ b/lore/sicp/set.scm
@@ -0,0 +1,42 @@
+;; A set module, based on binary trees (from sicp)
+
+(define (entry tree) (car tree))
+(define (left-branch tree) (cadr tree))
+(define (right-branch tree) (caddr tree))
+
+(define (make-tree entry left right)
+ (list entry left right))
+
+(define (element-of-set? x set)
+ (cond ((null? set) #f)
+ ((= x (entry set)) #t)
+ ((< x (entry set))
+ (element-of-set? x (left-branch set)))
+ ((> x (entry set))
+ (element-of-set? x (right-branch set)))))
+
+(define (adjoin-set x set)
+ (cond ((null? set) (make-tree x '() '()))
+ ((= x (entry set)) set)
+ ((< x (entry set))
+ (make-tree (entry set)
+ (adjoin-set x (left-branch set))
+ (right-branch set)))
+ ((> x (entry set))
+ (make-tree (entry set)
+ (left-branch set)
+ (adjoin-set x (right-branch set))))))
+
+(define (intersection-set set1 set2)
+ (if (or (null? set1) (null? set2))
+ '()
+ (let ((x1 (car set1))
+ (x2 (car set2)))
+ (cond ((= x1 x2)
+ (cons x1
+ (intersection-set (cdr set1)
+ (cdr set2))))
+ ((< x1 x2)
+ (intersection-set (cdr set1) set2))
+ ((< x2 x1)
+ (intersection-set set1 (cdr set2)))))))