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copied!<p>Project Euler Problem number 2: <a href="http://projecteuler.net/problem=2" rel="nofollow">http://projecteuler.net/problem=2</a></p> <p>Haskell (functional/logic):</p> <pre><code>p2 = sum [x | x <- fibs, (x `mod` 2) == 0] where fibs = unfoldr acc (0,1) where acc (prev, cur) | (prev+cur) > 4000000 = Nothing | otherwise = Just (prev+cur, (cur, prev+cur)) </code></pre> <p>Python (OO):</p> <pre><code>class FibSum(object): def __init__(self, end): self.end = end self.next_two = (1,0) self.sum = 0 def __iter__(self): return self def next(self): current, previous = self.next_two self.next_two = (previous+current, current) new = current+previous if current >= self.end: raise StopIteration elif (new % 2) == 0: self.sum += new else: pass fibcount = FibSum(4000000) [i for i in fibcount] print fibcount.sum </code></pre> <p>C (procedural/imperative):</p> <pre><code>#include <stdio.h> int main(void) { long int sum, newnum, previous = 0; long int current = 1; while(current <= 4000000) { newnum = previous+current; if ((newnum % 2) == 0) { sum = sum + newnum; } previous = current; current = newnum; } printf("%d\n", sum); } </code></pre> <p>And here is a very inefficient version written in MIT Scheme</p> <pre><code>(define (unfold func seed) (let* ((result (func seed))) (cond ((null? result) ()) (else (cons (car result) (unfold func (second result))))))) (define (test x) (cond ((> (sum x) 4000000) ()) (else (list (sum x) (list (second x) (sum x)))))) (define (sum xs) (cond ((null? (cdr xs)) (first xs)) (else (+ (car xs) (sum (cdr xs)))))) (sum (filter (lambda (x) (eq? (modulo x 2) 0)) (unfold test (list 0 1)))) </code></pre> <p>Prolog: <a href="http://snipd.net/prolog-project-euler-problem-2" rel="nofollow">Take from this here, posted by 13tazer31</a></p> <pre><code>fibonacci(_,Current,End,0) :- Current > End. fibonacci(Previous, Current, End, Total) :- divisible(Current, 2), Next is Current + Previous, fibonacci(Current, Next, End, Sum), Total is Sum + Current, !. fibonacci(Previous, Current, End, Total) :- Next is Current + Previous, fibonacci(Current, Next, End, Total). divisible(Number, 0) :- write(‘Error: division by 0′). divisible(Number, Divisor) :- Number mod Divisor =:= 0. </code></pre>

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