#lang racket
 
;(define (f lst)
;  (let loop ((a (car lst)) (b (cadr lst)) (lst (cddr lst)) (acc '()))
;    (if (null? lst)
;        (cons (+ a b) acc)
;        (loop b (car lst) (cdr lst) (cons (+ a b) acc)))))
;
;(define (pascal n)
;  (let loop ((n n) (acc '((1) (1 1))))
;    (cond ((zero? n) `(,(car acc)))
;          ((= n 1) acc)
;          (else (loop (- n 1) `(,@acc (1 ,@(f (last acc)) 1)))))))
 
;;; 別解
 
(define (pascal n)
  (foldl (lambda (y x)
           (cond ((zero? y) x)
                 ((= y 1) `(,@x (,y ,y)))
                 (else `(,@x (1 ,@(let ((lst (last x)))
                                    (map + (take lst (- (length lst) 1))
                                         (cdr lst))) 1)))))
         '((1)) (range 0 (+ n 1))))

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