cipher.lisp

;; Solution to https://uva.onlinejudge.org/external/112/p11220.pdf

(defun split-string (string &optional (sep-char #\space))
  (loop for i = 0 then (1+ j)
        for j = (position sep-char string :start i)
        collect (subseq string i j)
        while j))

(defun decode-line (str)
  (loop for word in (split-string str)
        with index = 0
        if (> (length word) index)
          collect (elt word index) into chars
          and do (incf index)
        finally (return (coerce chars 'string))))

(defun decode-file (file)
  (with-open-file (stream file)
    ;; Read and discard # of cases at top of file
    (read-line stream nil nil)
    (loop for line = (read-line stream nil nil)
          for case-sep = "" then (format nil "~%")
          with case-num = 0
          while line
          do (if (zerop (length line))
                 (format t "~ACase #~A~%" case-sep (incf case-num))
                 (format t "~A~%" (decode-line line))))))