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Project Euler problem 2

on project euler, erlang, perl, python

Even Fibonacci numbers

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.
Link to original description
Source code examples on Github

Erlang version 1

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#!/usr/bin/env escript
%% -*- erlang -*-
%%! -smp enable -sname p2
% vim:syn=erlang

-mode(compile).

main(_) ->
    Answer = lists:sum([X ||X <- fib([2,1]), X rem 2 =:= 0]),
    io:format("Answer ~p ~n",[Answer]).

fib([H|T]) when H >= 4000000 -> lists:reverse(T);    
fib([H1, H2| T]) -> fib([H1+H2, H1, H2|T]).

Erlang version 2

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#!/usr/bin/env escript
%% -*- erlang -*-
%%! -smp enable -sname p2_1
% vim:syn=erlang

-mode(compile).

main(_) ->
    Answer = fib(2,1,0),
    io:format("Answer ~p ~n",[Answer]).

fib(A,B,S) when A >= 4000000, B rem 2 =:= 0 -> B+S;
fib(A,_,S) when A >= 4000000  -> S;
fib(A,B,S) when B rem 2 =:= 0 -> fib(A+B, A, B+S);
fib(A,B,S) -> fib(A+B, A, S).

Perl version

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#!/usr/bin/perl -w

use strict;


sub main{
    my @fib_array = (1,2);
    my $sum = 0;
    while(1){
        my $new_value = $fib_array[$#fib_array] + $fib_array[$#fib_array-1];
        last if $new_value > 4000000;
        push @fib_array, $new_value;
    }
    for(grep{ !($_%2) } @fib_array){ $sum += $_ }
    print "Answer:  $sum \n"
}

main();

Python version

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#!/usr/bin/python

def main():
    answer = 2
    fib_a  = 2
    fib_b  = 1

    while fib_a < 4000000:
        fib_a, fib_b = fib_a + fib_b, fib_a
        if fib_a % 2 == 0: answer += fib_a 

    print "Answer %d " % answer

main()