http://www.reddit.com/r/dailyprogrammer/comments/psf4n/21620

<?php
while (1) {
    echo "INPUT ZERO-BASED COORDINATES\n";
    $handle = fopen("php://stdin", "r");
    $line = fgets($handle);
    $coords = explode(', ', trim($line));
    if (!preg_match('/^\d+$/', $coords[0]) && !preg_match('/^\d+$/', $coords[1])) {
        die("INVALID INPUT\n");
    }

    echo "RESULT: " . calculate($coords[1], $coords[0]) . "\n";
}

function calculate($x, $y) {
    static $triangle;
    if (($x == 0) || ($x == $y)) {
        return 1;
    }
    if ($x > $y) {
        return 0;
    }
    if (!isset($triangle[$y - 1][$x])) {
        $triangle[$y - 1][$x] = calculate($x, $y - 1);
    }
    if (!isset($triangle[$y - 1][$x - 1])) {
        $triangle[$y - 1][$x - 1] = calculate($x - 1, $y - 1);
    }
    return ($triangle[$y - 1][$x] + $triangle[$y - 1][$x - 1]);
}

?>