Solution for the Code Jam's problem "All Your Base" (https://code.google.com/codejam/contest/189252/dashboard#s=p0)

all-your-base.lisp

#!/usr/bin/sbcl --script

(defun count-unique (alist)
  (let ((hash (make-hash-table :test #'equal)))
    (map 'nil
         (lambda (i)
           (setf (gethash i hash) 1))
         alist)
    (hash-table-count hash)))

(defun determine-number (digits)
  (let ((hash (make-hash-table :test #'equal))
        (current 0)
        (total 0)
        (size (length digits))
        (base (count-unique digits)))
    (setf base (if (= base 1) 2 base))
    (setf (gethash (elt digits 0) hash) 1)
    (loop for i from 0 below size
       for x = (- size 1) then (1- x)
       for d = (elt digits i)
       do
         (unless (gethash d hash)
           (setf (gethash d hash) current)
           (incf current)
           (when (= current 1) (incf current)))
         (incf total (* (gethash d hash) (expt base x))))
    total))

(with-open-file (in (car (last *posix-argv*)))
  (let ((total-cases (read in)))
    (with-open-file (out "A.out" :direction :output :if-exists :supersede)
      (loop for i from 1 to total-cases
         do
           (let ((test-case (read-line in)))
             (format out "Case #~D: ~D~%" i (determine-number test-case)))))))