Just-the-Facts.php

<?php
function bcfact($n){
    $factorial=$n;
    while (--$n > 1) {
        $factorial = bcmul($factorial,$n);
    }
    return $factorial;
}

function getFileContent()
{
    $file = 'input.txt';
    return array_filter(explode(PHP_EOL, file_get_contents($file)));
}

function run()
{
    $numbers = getFileContent();
    foreach ($numbers as $number) {
        $output[] = $number . ' -> ' . substr(trim(bcfact($number),0), -1);
    }
    file_put_contents('output.txt', implode(PHP_EOL, $output));
}
$eStart = microtime(true);
run();
$eEnd = microtime(true);
echo 'Execution time: ' . ($eEnd - $eStart) * 1000 . ' ms' . PHP_EOL;