Question

How to check if a number can be made prime by deleting a single digit in PHP

Answer 1

function remove_the_N_digit($num, $N) {
    $num_str = strval($num);
    
    return intval(substr($num_str, 0, $N) . substr($num_str, $N+1));
}

function is_prime($n) {
    if ($n < 2 || ($n % 2 == 0 && $n != 2)) {
        return false;
    }
    
    $count = intval(sqrt($n));
    for ($i = 3; $i <= $count; $i += 2) {
        if ($n % $i == 0) {
            return false;
        }
    }
    
    return true;
}

$n = 78919;
$total_digits = intval(strlen(strval($n)));

for ($i = 0; $i < $total_digits; $i++) {
    $tmp = remove_the_N_digit($n, $i);
    if (is_prime($tmp)) {
        echo "yes number = " . $tmp;
        break;
    }
}


/*
run:
 
yes number = 7919
 
*/

 

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