Find The K-th Lucky Number

class Solution {
public:
    string kthLuckyNumber(long long k) {
        k += 1;
        string bits;
        while (k) { bits.push_back('0' + (k & 1)); k >>= 1; }
        bits.pop_back(); // drop leading 1
        reverse(bits.begin(), bits.end());
        for (char& c : bits) c = (c == '0') ? '6' : '8';
        return bits;
    }
};

func kthLuckyNumber(k int64) string {
    k += 1
    bits := []byte{}
    for k > 0 {
        bits = append(bits, byte('0'+(k&1)))
        k >>= 1
    }
    bits = bits[:len(bits)-1] // drop leading 1
    // reverse
    for i, j := 0, len(bits)-1; i < j; i, j = i+1, j-1 {
        bits[i], bits[j] = bits[j], bits[i]
    }
    for i, c := range bits {
        if c == '0' {
            bits[i] = '6'
        } else {
            bits[i] = '8'
        }
    }
    return string(bits)
}

class Solution:
    def kthLuckyNumber(self, k: int) -> str:
        k += 1
        bits = bin(k)[3:]  # drop '0b' and the leading 1
        return ''.join('6' if c == '0' else '8' for c in bits)

var kthLuckyNumber = function(k) {
    k += 1;
    let bits = k.toString(2).slice(1); // drop leading 1
    let out = '';
    for (const c of bits) out += (c === '0') ? '6' : '8';
    return out;
};

class Solution {
    public String kthLuckyNumber(long k) {
        k += 1;
        String bits = Long.toBinaryString(k).substring(1); // drop leading 1
        StringBuilder out = new StringBuilder();
        for (int i = 0; i < bits.length(); i++) {
            out.append(bits.charAt(i) == '0' ? '6' : '8');
        }
        return out.toString();
    }
}

function kthLuckyNumber(k: number): string {
    k += 1;
    const bits = k.toString(2).slice(1); // drop leading 1
    let out = '';
    for (const c of bits) out += (c === '0') ? '6' : '8';
    return out;
}