1. 1.string -> int: atoi(str.c_str()) / stoi(str)

    int -> string: to_string(num)

    1. 局部最优到整体最优
    2. 排序问题
    1.     static bool compare(int num1, int num2){
    2.         string s1 = to_string(num1) + to_string(num2);
    3.         string s2 = to_string(num2) + to_string(num1);
    4.         //检查越界
    5.         int n = s1.length();
    6.         for(int i = 0;i < n;++i){
    7.             if(s1[i] < s2[i])return true;
    8.             else if(s1[i] > s2[i])return false;
    9.         }
    10.         return false;
    11.     }
    12.     string PrintMinNumber(vector<int> numbers) {
    13.         string ans = "";
    14.         if(numbers.empty())return ans;
    15.         sort(numbers.begin(), numbers.end(), compare);
    16.         for(int num : numbers){
    17.             ans += to_string(num);
    18.         }
    19.         return ans;
    20.     }