Euler Project Two

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.

Here is my solution

(defun fib(n)

  (fib-iter 1 0 n))

(defun fib-iter(a b count_)

  (if (= count_ 0)

      b

      (fib-iter (+ a b) a (- count_ 1))))

(defun GenerateList(n)

  (if (< (fib n) 4000000)

      (cons (fib n) (GenerateList (+ n 1)))))

(defun FilterEuler2List(seq)

  (if (null seq)

      nil

      (if (evenp (car seq))

        (cons (car seq) (FilterEuler2List (cdr seq)))

          (FilterEuler2List (cdr seq)))))

;(apply #'+ (FilterEuler2List (GenerateList 0))

Solution one

(defun list-fibs (limit) 
(let ((fibs '(2 1))) 
(do ((nextfib (+ (car fibs) (cadr fibs)) 
(+ (car fibs) (cadr fibs)))) 
((> nextfib limit)) 
(setq fibs (cons nextfib fibs))) 
fibs)) 

(defun euler2 () 
(reduce #'+ (remove-if-not #'evenp (list-fibs 1000000)))) 

Solution two

(loop 
for x = 1 then y 
and y = 2 then (+ x y) 
and z = 0 then (1+ z) 
do (when (>= y 1000000) (return total)) 
when (evenp y) 
sum y into total 
end 
)

Solution Three

(defun problem-2 () 
(loop for x = 1 then y 
and y = 2 then (+ x y) 
while (< x 1000000) 
when (evenp x) 
sum x))

Solution Four

(defun fib (x &optional (y 0) (z 1))
(if (< x z)
nil
(append (list z) (fib x z (+ y z)))))
 
(reduce #'+ (remove-if-not #'evenp (fib 1000000)))