Question

How to check if every digit in a number appears only once in PHP

Answer 1

// n % 10 extracts the last digit.
// 1 << digit creates a bitmask for that digit.
// mask & bit checks whether the bit for this digit is already set.
// Mark the digit as seen: mask |= bit; This sets the bit for the current digit.

function allDigitsUnique(int $n): bool {
    $mask = 0;

    while ($n > 0) {
        $digit = $n % 10;
        $bit = 1 << $digit;

        if ($mask & $bit) {
            return false; // digit already seen
        }
        $mask |= $bit;

        $n = intdiv($n, 10);
    }

    return true;
}

$n = 123456;
echo allDigitsUnique($n) ? "Unique\n" : "Not unique\n";

$n = 123452;
echo allDigitsUnique($n) ? "Unique\n" : "Not unique\n";



/*
run:

Unique
Not unique

*/

 

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