剑指offer--32.把数组排成最小的数

class Solution {
    public:
        string PrintMinNumber(vector<int> numbers) {
            int len = numbers.size();
            if(len == 0) return "";
            sort(numbers.begin(), numbers.end(), cmp);
            string res;
            for(int i = 0; i < len; i++) {
                res += to_string(numbers[i]);
            }
            return res;
        }
        static bool cmp(int a, int b) {
            string A = to_string(a) + to_string(b);
            string B = to_string(b) + to_string(a);
            return A < B;
        }
};