30. Largest Number

class Solution:
    def largestNumber(self, nums: List[int]) -> str:
        s = [str(x) for x in nums]
        # a goes before b when a+b is the bigger concatenation
        s.sort(key=functools.cmp_to_key(lambda a, b: -1 if a + b > b + a else (1 if a + b < b + a else 0)))
        res = ''.join(s)
        return '0' if res[0] == '0' else res

class Solution {
    public String largestNumber(int[] nums) {
        String[] s = new String[nums.length];
        for (int i = 0; i < nums.length; i++) s[i] = String.valueOf(nums[i]);
        Arrays.sort(s, (a, b) -> (b + a).compareTo(a + b));   // a first when a+b is bigger
        if (s[0].equals("0")) return "0";
        return String.join("", s);
    }
}

class Solution {
public:
    string largestNumber(vector<int>& nums) {
        vector<string> s;
        for (int x : nums) s.push_back(to_string(x));
        sort(s.begin(), s.end(), [](const string& a, const string& b) { return a + b > b + a; });
        if (s[0] == "0") return "0";
        string res;
        for (auto& x : s) res += x;
        return res;
    }
};

function largestNumber(nums) {
  const s = nums.map(String).sort((a, b) => (b + a).localeCompare(a + b)); // a first when a+b is bigger
  return s[0] === '0' ? '0' : s.join('');
}