X-Git-Url: https://git.rkrishnan.org/?p=sicp.git;a=blobdiff_plain;f=src%2Fsicp%2Fsudoku.rkt;fp=src%2Fsicp%2Fsudoku.rkt;h=88dc92680b117d70ffee591394ff7c7bdfbf74c5;hp=0000000000000000000000000000000000000000;hb=273f2bd230187a3164803ac32d9b5734d0123ad0;hpb=c3062a9e8691e9c067b69ec24a728c746520b310

diff --git a/src/sicp/sudoku.rkt b/src/sicp/sudoku.rkt
new file mode 100644
index 0000000..88dc926
--- /dev/null
+++ b/src/sicp/sudoku.rkt
@@ -0,0 +1,61 @@
+#lang racket
+
+(require "amb-eli.rkt"
+         "distinct.rkt")
+
+(define (positions size)
+  (for*/list ([x (in-range 1 (+ size 1))]
+              [y (in-range 1 (+ size 1))])
+    (list x y)))
+
+;; board is represented as list of lists
+;;
+
+(define (sudoku board)
+  (let ([size (length board)])
+    (let ([new-board (amb-board board)])
+      (for ([r new-board])
+        (assert (distinct? r)))
+      (for ([c (apply map list new-board)])
+        (assert (distinct? c)))
+      (let ([ss (segments size)])
+        (for ([s ss])
+          (assert (distinct? s)))
+        new-board))))
+
+
+(define (amb-board board)
+  (cond [(empty? board) empty]
+        [else 
+         (let ([row (first board)])
+           (cons (for/list ([r row])
+                   (if (eq? r '?)
+                       (amb-list (set->list (set-subtract (set 1 2 3 4 5 6 7 8 9) (list->set row))))
+                       r))
+                 (amb-board (rest board))))]))
+
+(define (segments board)
+  (let ([size (length board)])
+    (let ([s (sqrt size)])
+      (for*/list ([i (in-range 0 size s)]
+                  [j (in-range 0 size s)])
+        (for*/list ([x (in-range i (+ i s))]
+                    [y (in-range j (+ j s))])
+          (list-ref (list-ref board x) y))))))
+
+
+
+#|
+
+((? ? 8 ? ? ? 1 5 ?)
+ (? ? ? ? ? 1 8 ? ?)
+ (3 ? 5 4 ? ? ? ? 9)
+ (5 ? ? ? ? 9 ? ? ?)
+ (? 9 ? 2 3 4 ? 7 ?)
+ (? ? ? 1 ? ? ? ? 8)
+ (4 ? ? ? ? 5 9 ? 1)
+ (? ? 6 7 ? ? ? ? ?)
+ (? 5 3 ? ? ? 2 ? ?))
+
+|#
+