Question

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

Answer 1

using System;

class UniqueDigits
{
    // 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.
    static bool AllDigitsUnique(int n) {
        int mask = 0;

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

            if ((mask & bit) != 0)   // digit already seen
                return false;

            mask |= bit;             // mark the digit as seen
            n /= 10;
        }

        return true;
    }

    static void Main()
    {
        int n = 123456;
        Console.WriteLine(AllDigitsUnique(n) ? "Unique" : "Not unique");

        n = 123452;
        Console.WriteLine(AllDigitsUnique(n) ? "Unique" : "Not unique");
    }
}



/*
run:

Unique
Not unique

*/

 

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