Given a list of non negative integers, arrange them such that they form the largest number.

For example, given [3, 30, 34, 5, 9], the largest formed number is 9534330.

Note: The result may be very large, so you need to return a string instead of an integer.

字符串排序，排序規則如下：

對于a和b兩個數字，如果ab>ba則a應該排在b之前

注意全為0的情況

class Solution {public:    static bool cmp(string &a, string &b)    {        return a+b > b+a;    }    string largestNumber(vector<int>& nums)     {        vector<string> res;        for(int i = 0; i < nums.size(); i++)            res.push_back(to_string(nums[i]));        sort(res.begin(), res.end(), cmp);        string ans;        for(int i = 0; i < res.size() ; i++) ans += res[i];        if(ans[0] == '0') ans = '0';        return ans;    }};