Given an array of elements find the largest possible number that can 

be formed by using the elements of the array. 

eg: 10 9 

ans: 910 

2 3 5 78 

ans: 78532 

100 9 

ans: 9100

把字符串排个序，比较方法是循环比较各个字符，如果对应位的字符大于另一个字符串的对应位则返回true，否则false。思想就是类似于要把尽可能大的数位放在更高位。

1 #include 
     
       2 #include 
      
        3 #include 
       
         4 #include 
        
          5 using namespace std; 6  7 bool comp(const string &lhs, const string &rhs) 8 { 9     int len = max(lhs.size(), rhs.size());10 11     for(int i = 0; i < len; i++)12     {13         int lIndex = i % lhs.size();14         int rIndex = i % rhs.size();15         if (lhs[lIndex] > rhs[rIndex])16             return true;17         else if (lhs[lIndex] < rhs[rIndex])18             return false;19     }20 21     return true;22 }23 24 string solve(vector
         
           &a)25 {26     sort(a.begin(), a.end(), comp);27 28     string s;29 30     for(int i = 0; i < a.size(); i++)31         s = s + a[i];32 33     return s;34 }35 36 int main()37 {38     vector
          
            a;39 a.push_back("10");40 a.push_back("9");41 cout << solve(a) << endl;42 43 vector
           
             b;44 b.push_back("2");45 b.push_back("3");46 b.push_back("5");47 b.push_back("78");48 cout << solve(b) << endl;49 50 vector
            
              c;51 c.push_back("100");52 c.push_back("9");53 cout << solve(c) << endl;54 }