Facebook Hacker Cup Double Squares

dsquares.lisp

(defparameter *lines* (with-open-file (in "input.txt")
			(loop for line = (read-line in nil nil)
			   while line
			   collect line into lines
			   finally (return lines))))

(defparameter *numbers* (mapcar #'read-from-string (cdr *lines*)))

(defun perfectp (x)
  (zerop (mod (sqrt x) 1)))

(defun expressions (n)
  (loop for i from 0 to (truncate (sqrt (/ n 2)))
       count (perfectp (- n (expt i 2)))))

(with-open-file (out "output.txt"
		     :direction :output
		     :if-exists :supersede)
  (with-standard-io-syntax
    (format out "~{~a~%~}" (mapcar #'expressions *numbers*))))