「数を作る」をSchemeで(横へな9参考) ref: http://qiita.com/pazworld/items/226324031ed86a6b284c

combi.scm

;; 与えられた整数リストから4つを使った全組み合わせを返す
(define (combi4 unselected selected)
  (define (delete-one x ls) ;; xを1つだけ削除したリストを返す
    (cond
     ((null? ls) '())
     ((= x (car ls)) (cdr ls))
     (else (cons (car ls) (delete-one x (cdr ls))))))
  (define (if6append9 x f) ;; xが6以外ならf(x)を、6ならf(6)とf(9)を連結して返す
    (if (= x 6)
        (append (f 6) (f 9))
        (f x)))
  (define (nextlevel x results) ;; 数を1つ組み合わせて次の桁へ進む
    (append
     (if6append9
      x
      (lambda (y)
        (combi4 (delete-one x unselected)
                (cons y selected)))) results))
  (if (= 4 (length selected))
      (list selected)
      (fold nextlevel '() unselected)))

;; リストの全組み合わせからn番目の整数を返す
(define (solve2 n ls)
  (define (list->num ls) ;; [1,1,0,9] -> 1109
    (fold (lambda (x s) (+ x (* s 10))) 0 ls))
  (define (take-n x over ls) ;; n番目があればその値、なければoverに指定された値を返す
    (if (> x (length ls))
        over
        (car (drop ls (- x 1)))))
  (take-n n '- (filter
             (lambda (x) (>= x 1000))
             (sort (delete-duplicates
                    (map list->num 
                         (combi4 ls '()))) <))))

;; 文字列を与えると問題を解く
(define (solve s)
  (define (char->number c)
    (- (char->integer c) (char->integer #\0)))
  (define (colon-idx)
    (string-search-forward ":" s))
  (define (get-n)
    (string->number (string-head s (colon-idx))))
  (define (get-numlist)
    (map
     char->number
     (string->list
      (substring s (+ 1 (colon-idx)) (string-length s)))))
  (solve2 (get-n) (get-numlist)))

;; テスト
(define (test data expected)
  (define (eq a b) ;; 数値または-を比較する
    (if (symbol? a) (eq? a b) (= a b)))
  (format #t "~A: ~A -> ~A~%"
          (if (eq expected (solve data)) "ok" "ng")
          data expected))

(define (tests)
  (begin
    (test "13:01167" 1109)
    (test "1:1234" 1234)
    (test "13:01167" 1109)
    (test "1:1234" 1234)
    (test "2:1234" 1243)
    (test "7:1234" 2134)
    (test "24:1234" 4321)
    (test "25:1234" '-)
    (test "2:1116" 1119)
    (test "2:0116" 1019)
    (test "3:6666" 6696)
    (test "16:6666" 9999)
    (test "10:01267" 1097)
    (test "14:111167" 1671)
    (test "1:1111" 1111)
    (test "2:1111" '-)
    (test "1:666633" 3366)
    (test "72:666611" 9999)
    (test "73:666622" '-)
    (test "1:666600" 6006)
    (test "52:666600" 9999)
    (test "53:666600" '-)
    (test "25:06688" 8086)
    (test "93:02566" 6502)
    (test "11:06688" 6809)
    (test "169:01268" 9801)
    (test "174:01268" 9821)
    (test "66:012288" 8201)))

(tests)