class Solution {
public:
    string largestNumber(vector<int> &num) {
        vector<string> str_num;
        // map num to string vector
        transform(num.begin(), num.end(), back_inserter(str_num),
            [](int i) { return to_string(i); });
        // sort by string
        sort(str_num.begin(), str_num.end(), [](string a, string b) {
            return b + a < a + b;
        });

        // edge case: all zeros
        if (str_num[0] == "0")
            return "0";

        // otherwise, join
        return accumulate(str_num.begin(), str_num.end(), string());
    }
};