Leetcode: Integer to Roman

http://oj.leetcode.com/problems/integer-to-roman/

class Solution {
public:
    string intToRoman(int num, int pos){
        char *cc="IVXLCDM  ";
        string res;
        char a=cc[pos*2],b=cc[pos*2+1],c=cc[pos*2+2];
        if(num<=3){
            for(int i=0;i<num;i++) res.push_back(a);
        }
        else if(num==4) {
            res.push_back(a);
            res.push_back(b);
        }
        else if(num<=8){
            res.push_back(b);
            for(int i=0;i<num-5;i++) res.push_back(a);
        }
        else if(num==9){
            res.push_back(a);
            res.push_back(c);
        }
        return res;
    }
    string intToRoman(int num) {
        // Note: The Solution object is instantiated only once and is reused by each test case.    
        int len=0;
        int numTmp=num;
        while(numTmp!=0) {numTmp/=10;len++;}
        vector<string> res;
        for(int i=0;i<len;i++){
            res.push_back(intToRoman(num%10,i));
            num/=10;
        }
        string output;
        for(int i=res.size()-1;i>=0;i--) output+=res[i];
        return output;
    }
};