Question

How to generate a random integer from a range [0, N] that is not in a unique integer list with PHP

Answer 1

function randomExcluding(int $N, array $excluded): int {
    if (count($excluded) > $N + 1) {
        return -1; // All numbers are excluded
    }

    do {
        $num = random_int(0, $N); // cryptographically secure and inclusive
    } while (in_array($num, $excluded));

    return $num;
}

$excluded = [2, 5, 7];
$N = 14;

echo randomExcluding($N, $excluded) . PHP_EOL;



/*
run:

9

*/

 

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