1.12.scm

;;;; 1.12
;; The following pattern of numbers is called Pascal's triangle.
;;
;;       1
;;      1 1
;;     1 2 1
;;    1 3 3 1
;;   1 4 6 4 1
;;
;; The numbers at the edge of the triangle are all 1, and each number inside the triangle is the sum of the two numbers above it. Write a procedure that computes elements of Pascal's triangle by means of a recursive process.

;;; Answwer
(define (pascal r c)
  (if (or (< r 1) (< c 1) (< r c)) 0
    (if (or (= c 1) (= c r)) 1
      (+ (pascal (- r 1) (- c 1))
         (pascal (- r 1) c)))))