剑指offer——把数组排成最小的数

#include <iostream>
#include <vector>
#include <string>
#include <sstream> 
#include <algorithm>
using namespace std;

class Solution {
    public:
        static int cmp(int a,int b){
            ostringstream s1,s2;
            s1<<a;
            s2<<b;
            string A = s1.str()+s2.str();
            string B = s2.str()+s1.str();
            return A<B;
        }

        string PrintMinNumber(vector<int> numbers) {
            int len = numbers.size();
            string ans = "";
            if(numbers.size() == 0){
                return ans;
            }
            sort(numbers.begin(),numbers.end(),cmp);
            for(int i = 0 ; i < len ; i++){
                ostringstream s;
                s<<numbers[i];
                ans += s.str();
            }
            return ans;
        }
};