A working implementation of elimination/trial and error solver

src/ray1729/clojure/sudoku/core.clj

@@ -29,9 +29,7 @@
 	col-map (into {} (for [ps (partition 3 cols) e ps] [e ps]))]
     (for [row (row-map r) col (col-map c)] (str row col))))
 
-(defn units [s] (vector (row-keys s) (col-keys s) (box-keys s)))
+(defn peers [s] (disj (into #{} (concat (row-keys s) (col-keys s) (box-keys s))) s))
-
-(defn peers [s] (disj (into #{} (apply concat (units s))) s))
 
 (declare assign)
 (declare eliminate)
@@ -58,24 +56,27 @@
 (defn solved? [grid]
   (every? #(= 1 (count %)) (vals grid)))
 
+(defn try-assign [grid cell value]
+  (ekit/with-handler
+    (assign grid cell value)
+    (ekit/handle *inconsistent-grid* [] nil)))
+
+(defn try-eliminate [grid cell value]
+  (ekit/with-handler
+    (eliminate grid cell value)
+    (ekit/handle *inconsistent-grid* [] nil)))
+
 (defn solve [grid]
-  (if (solved? grid)
+  (when grid
-    grid
+    (if (solved? grid)
-    (let [cell (first (filter #(> (count (grid %)) 1) (keys grid)))
+      grid
-	  candidates (grid cell)
+      (let [cell (first (filter #(> (count (grid %)) 1) (keys grid)))
-	  candidate (first candidates)]
+	    value (first (grid cell))]
-      (ekit/with-handler
+	(or (solve (try-assign grid cell value)) (solve (try-eliminate grid cell value)))))))
-	(do
-	  (println (str "Trying " cell "=" candidate))
-	  (recur (assign grid cell candidate)))
-	(ekit/handle *inconsistent-grid* []		     
-		     (if (next candidates)
-		       (do (println (str "Trying next candidate for " cell))
-			   (recur (eliminate grid cell candidate)))
-		       (ekit/do-not-handle)))))))
 
 (comment
   
+  ;; This is a trivial puzzle: it is solved by the initial assignment
   (def g1 (parse-grid
 	   "003020600
             900305001
@@ -87,5 +88,67 @@
             800203009
             005010300"))
 
+  (solved? g1)
+  ;;=> true
+
   (def g2 (parse-grid "400000805030000000000700000020000060000080400000010000000603070500200000104000000"))
+
+  (print-grid g2)
+;; ...4..... 1....67.9 12...67.9 | 1.3.....9 .23..6..9 12...6..9 | .......8. 123.....9 ....5....
+;; .2...6789 ..3...... 12..56789 | 1..45..89 .2.456..9 12.456.89 | 12...67.9 12.4....9 12.4.67.9
+;; .2...6.89 1...56.89 12..56.89 | ......7.. .23456..9 12.456.89 | 123..6..9 1234....9 1234.6..9
+;; ------------------------------+-------------------------------+------------------------------
+;; ..3...789 .2....... 1.3.5.789 | ..345...9 ..345.7.9 ...45.7.9 | 1.3.5.7.9 .....6... 1.3...789
+;; ..3..67.9 1...567.9 1.3.567.9 | ..3.5...9 .......8. .2..567.9 | ...4..... 123.5...9 123...7.9
+;; ..3..6789 ...456789 ..3.56789 | ..345...9 1........ .2.4567.9 | .23.5.7.9 .23.5..89 .23...789
+;; ------------------------------+-------------------------------+------------------------------
+;; .2.....89 .......89 .2.....89 | .....6... ...45...9 ..3...... | 12..5...9 ......7.. 12.4...89
+;; ....5.... .....6789 ..3..6789 | .2....... ...4..7.9 1..4..789 | 1.3..6..9 1.34...89 1.34.6.89
+;; 1........ .....6789 ...4..... | ....5..89 ....5.7.9 ....5.789 | .23.56..9 .23.5..89 .23..6.89  
+  
+  ;; More tricky...
+  (solved? g2)
+  ;;=> false
+
+  (def s (solve g2))
+  (solved? s)
+  ;;=> true
+
+  (print-grid s)
+;; ...4..... 1........ ......7.. | ..3...... .....6... ........9 | .......8. .2....... ....5....
+;; .....6... ..3...... .2....... | 1........ ....5.... .......8. | ........9 ...4..... ......7..
+;; ........9 ....5.... .......8. | ......7.. .2....... ...4..... | ..3...... 1........ .....6...
+;; ------------------------------+-------------------------------+------------------------------
+;; .......8. .2....... ....5.... | ...4..... ..3...... ......7.. | 1........ .....6... ........9
+;; ......7.. ........9 1........ | ....5.... .......8. .....6... | ...4..... ..3...... .2.......
+;; ..3...... ...4..... .....6... | ........9 1........ .2....... | ......7.. ....5.... .......8.
+;; ------------------------------+-------------------------------+------------------------------
+;; .2....... .......8. ........9 | .....6... ...4..... ..3...... | ....5.... ......7.. 1........
+;; ....5.... ......7.. ..3...... | .2....... ........9 1........ | .....6... .......8. ...4.....
+;; 1........ .....6... ...4..... | .......8. ......7.. ....5.... | .2....... ........9 ..3......
+  
+  (def g3 (parse-grid
+	   "008601000
+            600000003
+            000048506
+            040000600
+            780020091
+            001000030
+            109870000
+            200000007
+            000209100"))
+
+  (print-grid (solve g3))
+;; ...4..... ..3...... .......8. | .....6... ....5.... 1........ | .2....... ......7.. ........9
+;; .....6... 1........ ....5.... | ......7.. ........9 .2....... | .......8. ...4..... ..3......
+;; ........9 .2....... ......7.. | ..3...... ...4..... .......8. | ....5.... 1........ .....6...
+;; ------------------------------+-------------------------------+------------------------------
+;; ..3...... ...4..... .2....... | ........9 1........ ......7.. | .....6... ....5.... .......8.
+;; ......7.. .......8. .....6... | ....5.... .2....... ..3...... | ...4..... ........9 1........
+;; ....5.... ........9 1........ | ...4..... .......8. .....6... | ......7.. ..3...... .2.......
+;; ------------------------------+-------------------------------+------------------------------
+;; 1........ .....6... ........9 | .......8. ......7.. ....5.... | ..3...... .2....... ...4.....
+;; .2....... ....5.... ..3...... | 1........ .....6... ...4..... | ........9 .......8. ......7..
+;; .......8. ......7.. ...4..... | .2....... ..3...... ........9 | 1........ .....6... ....5....
+  
   )