Question

How to find the largest prime factor of a number in PHP

Answer 1

function largestPrimeFactor($n) {
    $div = 2;
    $maxPFact = -1;

    while ($n != 0) {
        if ($n % $div != 0) {
            $div++;
        } else {
            $maxPFact = $n;
            $n /= $div;
            if ($n == 1) {
                break;
            }
        }
    }

    return $maxPFact;
}

echo largestPrimeFactor(124) . "\n"; // 2 x 2 x 31
echo largestPrimeFactor(288) . "\n"; // 2 x 2 x 2 x 2 x 2 x 3 x 3
echo largestPrimeFactor(1288) . "\n"; // 2 x 2 x 2 x 7 x 23
echo largestPrimeFactor(100000000) . "\n"; // 2, 2, 2, 2, 2, 2, 2, 2, 5, 5, 5, 5, 5, 5, 5, 5



/*
run:

31
3
23
5

*/

 

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