X-Git-Url: https://git.rkrishnan.org/?p=sicp.git;a=blobdiff_plain;f=src%2Fsicp%2Fex4_37.rkt;fp=src%2Fsicp%2Fex4_37.rkt;h=a4528a0070e6777ecc900bb8dc05a419bea00ab8;hp=0000000000000000000000000000000000000000;hb=16ffd75b36a5dbfbda3da703c2732f8f49208c11;hpb=ef9bb63c4d3fa21f9964c3a5e612bfc519406744

diff --git a/src/sicp/ex4_37.rkt b/src/sicp/ex4_37.rkt
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+++ b/src/sicp/ex4_37.rkt
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+#lang racket
+
+(require "amb-eli.rkt")
+
+(define (a-pythagorean-triple-between low high)
+  (let ((i (an-integer-between low high))
+        (hsq (* high high)))
+    (let ((j (an-integer-between i high)))
+      (let ((ksq (+ (* i i) (* j j))))
+        (assert (>= hsq ksq))
+        (let ((k (sqrt ksq)))
+          (assert (integer? k))
+          (list i j k))))))
+
+#|
+
+Yes, Ben is correct. The above program prunes the search space by restricting the
+possible values of k.
+
+k^2 <= high^2
+
+and sqrt (i^2 + j^2) is an integer. This eliminates a large number of (i, j, k) triples
+and hence the search space is a lot less than the naive implementation in the text.
+
+|#