Question

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

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(n) {
    let mask = 0;

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

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

        n = Math.floor(n / 10);
    }

    return true;
}

let n = 123456;
console.log(allDigitsUnique(n) ? "Unique" : "Not unique");

n = 123452;
console.log(allDigitsUnique(n) ? "Unique" : "Not unique");



/*
run:

Unique
Not unique

*/

 

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