blob: 65b567de13ddd5e3e1212e69d59664a70e2b1bdf (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
|
;;;;
;; Even Fibonacci numbers
;; Problem 2
;;
;; Each new term in the Fibonacci sequence is generated by adding the previous two terms. By
;; starting with 1 and 2, the first 10 terms will be:
;; 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...
;; By considering the terms in the Fibonacci sequence whose values do not exceed four
;; million, find the sum of the even-valued terms.
;;;;
(load "utils.scm")
(define +top+ 4000000)
(define fib
(lambda (n)
(case n
((0) 1)
((1) 1)
(else (+ (fib (- n 1))
(fib (- n 2)))))))
(define result
(sum
(filter (lambda (x) (= 0 (modulo x 2)))
(do ((x 1 (+ x 1))
(f 1 (fib x))
(fs '()))
((>= f +top+) fs)
(set! fs (cons f fs))))))
(display result)
|
