euler.php

#!/usr/bin/env php
<?php

# Problem #1:
# Answer: 233168
#
# 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.
#
function euler1() {
   return array_sum(array_filter(range(3, 999),
                    create_function('$x',
                                    'return ($x % 3 == 0) || ($x % 5 == 0);')));
}


# Problem #2:
# Answer: 4613732
#
# 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.
#
function euler2() {
   $last1 = 2;
   $last2 = 1;
   $sum = 2;
   while (1) {
       $cur = $last1 + $last2;
       if ($cur > 4000000) {
           break;
       }
       if ($cur % 2 == 0) {
           $sum += $cur;
       }
       $last2 = $last1;
       $last1 = $cur;
   }
   return $sum;
}

$eulers = array(
    1 => euler1,
    2 => euler2,
);

if (isset($argc)) {
    // Main
    if ($argc == 1) {
        // No command line args passed, so run them all.
        foreach ($eulers as $num => $euler) {
            echo "#" . $num . ". " . $euler() . "\n";
        }
    } else {
        // Command line args passed, just run the requested ones.
        foreach (array_slice($argv, 1) as $arg) {
            echo "#" . $arg . ". " . eval('return euler' . $arg . '();') . "\n";
        }
    }
}
?>