Language: C C++ D Haskell Lua OCaml PHP Perl Plain Text Python Ruby Scheme Tcl ; damm algorithm ; http://en.wikipedia.org/wiki/Damm_algorithm (define (digits n . args) (let ((b (if (null? args) 10 (car args)))) (let loop ((n n) (d '())) (if (zero? n) d (loop (quotient n b) (cons (modulo n b) d)))))) (define damm '#( #(0 3 1 7 5 9 8 6 4 2) #(7 0 9 2 1 5 4 8 6 3) #(4 2 0 6 8 7 1 3 5 9) #(1 7 5 0 9 8 3 4 2 6) #(6 1 2 3 0 4 5 9 7 8) #(3 6 7 4 2 0 9 5 8 1) #(5 8 6 9 7 2 0 1 3 4) #(8 9 4 5 3 6 2 0 1 7) #(9 4 3 8 6 1 7 2 0 9) #(2 5 8 1 4 3 6 7 9 0))) (define (check num) (let loop ((d 0) (ds (digits num))) (if (null? ds) (+ (* num 10) d) (loop (vector-ref (vector-ref damm d) (car ds)) (cdr ds))))) (define (valid? num) (let loop ((d 0) (ds (digits num))) (if (null? ds) (zero? d) (loop (vector-ref (vector-ref damm d) (car ds)) (cdr ds))))) (display (check 572)) (newline) (display (valid? 5724)) (newline) Private [?] Run code Submit