isValidCPF.php

function isValidCPF($number)
{

    $number = preg_replace('/[^0-9]/', '', (string) $number);

    if (strlen($number) != 11)
        return false;

    for ($i = 0, $j = 10, $sum = 0; $i < 9; $i++, $j--)
        $sum += $number{$i} * $j;
    $rest = $sum % 11;
    if ($number{9} != ($rest < 2 ? 0 : 11 - $rest))
        return false;

    for ($i = 0, $j = 11, $sum = 0; $i < 10; $i++, $j--)
        $sum += $number{$i} * $j;
    $rest = $sum % 11;

    return ($number{10} == ($rest < 2 ? 0 : 11 - $rest));

}

// Após a versão 7.4 o uso de chaves ficou obsoleto, veja em: https://wiki.php.net/rfc/deprecate_curly_braces_array_access

function isValidCPF(string $number):bool {

$number = preg_replace('/[^0-9]/', '', (string) $number);

if (strlen($number) != 11)
    return false;

for ($i = 0, $j = 10, $sum = 0; $i < 9; $i++, $j--)
    $sum += $number[$i] * $j;
$rest = $sum % 11;
if ($number[9] != ($rest < 2 ? 0 : 11 - $rest))
    return false;

for ($i = 0, $j = 11, $sum = 0; $i < 10; $i++, $j--)
    $sum += $number[$i] * $j;
$rest = $sum % 11;

return ($number[10] == ($rest < 2 ? 0 : 11 - $rest));

}