three_letters_combination();
function three_letters_combination()
{
$s = "abcdefghijklmnopqrstuvwxyz0123456789";
$f = fopen("d:/three_letters_combination.txt", "a") or die("Error open file!");
$s_size = strlen($s);
for ($i = 0; $i < $s_size; $i++)
{
for ($j = 0; $j < $s_size; $j++)
{
for ($k = 0; $k < $s_size; $k++)
{
fwrite($f, $s[$i] . $s[$j] . $s[$k] . " ");
}
fwrite($f, "\r\n");
}
fwrite($f, "\r\n");
}
fclose($f);
echo "end. check the file.";
}
/*
run:
end. check the file.
*/