; Requirements:
; 0 <= r
; 0 <= c <= r
; Ouput:
; cth element of rth row of pascal's triangle
; ie: r choose c
(define (pascal r c)
  (cond ((= c 0) 1)
        ((= c r) 1)
        ((= r 0) 1)
        (else (+ (pascal (- r 1) (- c 1))
                 (pascal (- r 1) c)))))
; O(r) memory
; O(r choose c) time

; Dynamic programming
; O(rc) memory
; O(rc) time