Question

How to find a list of numbers up to a limit that is a palindrome in base 10 and base 2 in PHP

Answer 1

// Function to check if a number is a palindrome in a given base
function isPalindrome(int $num, int $base): bool {
    if ($base < 2) return false; // Invalid base

    $strnumReversed = '';
    $temp = $num;

    // Convert number to string in given base
    do {
        $digit = $temp % $base;
        $strnumReversed .= ($digit < 10) ? chr(ord('0') + $digit) : chr(ord('A') + ($digit - 10));
        $temp = intdiv($temp, $base);
    } while ($temp > 0);

    // Check palindrome
    return $strnumReversed === strrev($strnumReversed);
}


$limit = 1000;

echo "Numbers that are palindromes in both base 10 and base 2:\n";
for ($i = 1; $i <= $limit; $i++) {
    if (isPalindrome($i, 10) && isPalindrome($i, 2)) {
        echo "$i (binary: ";

        // Print binary representation
        $binary = '';
        $temp = $i;
        do {
            $binary .= ($temp % 2) ? '1' : '0';
            $temp = intdiv($temp, 2);
        } while ($temp > 0);

        $binary = strrev($binary);
        echo "$binary)\n";
    }
}



/*
run:

Numbers that are palindromes in both base 10 and base 2:
1 (binary: 1)
3 (binary: 11)
5 (binary: 101)
7 (binary: 111)
9 (binary: 1001)
33 (binary: 100001)
99 (binary: 1100011)
313 (binary: 100111001)
585 (binary: 1001001001)
717 (binary: 1011001101)

*/

 

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