test

csp/csp/hacs-cryptarithmetic.rkt

@@ -0,0 +1,40 @@
+#lang debug racket
+(require "hacs.rkt" sugar/debug)
+(module+ test (require rackunit))
+
+(define (word-value d str)
+    (define xs (for/list ([c (in-string str)])
+                 (dict-ref d (string->symbol (string c)))))
+    (for/sum ([(x idx) (in-indexed (reverse xs))])
+      (* x (expt 10 idx))))
+
+(define (math-csp str)
+  (define input str)
+  (define words (map string-downcase (string-split input)))
+  (match-define (list terms ... sum) words)
+  (define vars (map string->symbol (remove-duplicates (for*/list ([word words]
+                                                                  [c word])
+                                                        (string c)))))
+  (unless (<= (length vars) 10)
+    (raise-argument-error 'too-many-letters))
+
+  (define (not= x y) (not (= x y)))
+
+  (define math (make-csp))
+  (add-vars! math vars (range 0 10))
+  ;; all letters have different values
+  (add-pairwise-constraint! math not= vars)
+;; first letters cannot be zero
+  (define firsts (remove-duplicates (map (compose1 string->symbol string car string->list) words) eq?))
+  (for ([first firsts])
+    (add-constraint! math positive? (list first)))
+  (add-constraint! math (λ args
+                          (define dict (map cons vars args))
+                          (= (apply + (map (λ (w) (word-value dict w)) terms)) (word-value dict sum))) vars)
+  math)
+
+#;(solve (math-csp "TWO TWO FOUR"))
+#;(solve (math-csp "DUCK DUCK GOOSE"))
+#;(solve (math-csp "TICK TICK BOOM"))
+#;(solve (math-csp "SEND MORE MONEY"))
+#;(solve (math-csp "THIS THAT OTHER"))