Question

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

Answer 1

import Foundation

// 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.

func allDigitsUnique(_ n: Int) -> Bool {
    var n = n
    var mask = 0

    while n > 0 {
        let digit = n % 10
        let bit = 1 << digit

        if (mask & bit) != 0 { return false } // digit already seen
        mask |= bit

        n /= 10
    }

    return true
}

let tests = [123456, 123452]

for value in tests {
    print(allDigitsUnique(value) ? "Unique" : "Not unique")
}



/*
run:

Unique
Not unique

*/
         

 

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