exercise 4.44: another optimization, but still too slow

Author: gbordyugov

chapter4/chapter4.03.scm

@@ -375,18 +375,26 @@
           (let ((this-column (car columns))
                 (this-row    (car rows)))
             (this-ok? this-column this-row rest-columns rest-rows))))))
-  (let ((q1 (amb 1 2 3 4 5 6 7 8))
-        (q2 (amb 1 2 3 4 5 6 7 8))
-        (q3 (amb 1 2 3 4 5 6 7 8))
-        (q4 (amb 1 2 3 4 5 6 7 8))
-        (q5 (amb 1 2 3 4 5 6 7 8))
-        (q6 (amb 1 2 3 4 5 6 7 8))
-        (q7 (amb 1 2 3 4 5 6 7 8))
-        (q8 (amb 1 2 3 4 5 6 7 8)))
-    (let ((columns (list q1 q2 q3 q4 q5 q6 q7 q8))
-          (rows    (list  1  2  3  4  5  6  7  8)))
-      (require (ok-position? columns rows))
-      (list q1 q2 q3 q4 q5 q6 q7 q8))))
+  (let ((q1 (amb 1 2 3 4 5 6 7 8)))
+    (let ((q2 (amb 1 2 3 4 5 6 7 8)))
+      (require (distinct? (list q1 q2)))
+      (let ((q3 (amb 1 2 3 4 5 6 7 8)))
+        (require (distinct? (list q1 q2 q3)))
+        (let ((q4 (amb 1 2 3 4 5 6 7 8)))
+          (require (distinct? (list q1 q2 q3 q4)))
+          (let ((q5 (amb 1 2 3 4 5 6 7 8)))
+            (require (distinct? (list q1 q2 q3 q4 q5)))
+            (let ((q6 (amb 1 2 3 4 5 6 7 8)))
+              (require (distinct? (list q1 q2 q3 q4 q5 q6)))
+              (let ((q7 (amb 1 2 3 4 5 6 7 8)))
+                (require (distinct? (list q1 q2 q3 q4 q5 q6 q7)))
+                (let ((q8 (amb 1 2 3 4 5 6 7 8)))
+                  (require (distinct? (list q1 q2 q3 q4 q5 q6 q7 q8)))
+                  (let ((columns (list q1 q2 q3 q4 q5 q6 q7 q8))
+                        (rows    (list  1  2  3  4  5  6  7  8)))
+                    (require (distinct? (list q1 q2 q3 q4 q5 q6 q7 q8)))
+                    (require (ok-position? columns rows))
+                    (list q1 q2 q3 q4 q5 q6 q7 q8)))))))))))
 
 ;;
 ;; prototype of the functions above