ProjectEuler

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とりあえず2問だけ解いた。
使用言語はGauche。
Cとかで書けるようになりたい＞＜

Problem 1

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.

Find the sum of all the multiples of 3 or 5 below 1000.

(define (add-n-num n)
  (define (iter result count)
    (cond [(= n count) result]
	  [(= 0 (* (modulo count 3) (modulo count 5)))
	   (iter (+ result count) (+ count 1))]
	  [else (iter result (+ count 1))]))
  (iter 0 0))

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, ...

Find the sum of all the even-valued terms in the sequence which do not exceed four million.

;;フィボナッチ配列の定義
(define (fib n)
  (define (iter-fib a b count)
    (if (= count 0)
	b
	(iter-fib (+ a b) a (- count 1))))
  (iter-fib 1 1 n))
;;和を求める
(define (even-valued-fib-sum max-value)
  (define (iter-sum sum-of-terms count)
    (let1 fibonacci (fib count)
      (cond [(> fibonacci max-value) sum-of-terms]
	    [(even? (fib count)) (iter-sum (+ sum-of-terms fibonacci) (+ count 1))]
	    [else (iter-sum sum-of-terms (+ count 1))])))
  (iter-sum 0 1))

ちょっとずつ解いていこう。