Integer to Roman Solutions in C++

// Source : https://oj.leetcode.com/problems/integer-to-roman/
// Author : Hao Chen
// Date   : 2014-07-17



#include <stdlib.h>
#include <string>
#include <iostream>
using namespace std;

//greeding algorithm
string intToRoman(int num) {
    string symbol[] =   {"M","CM","D","CD","C","XC","L","XL","X","IX","V","IV","I"};    
    int value[]     =   {1000,900,500,400, 100, 90,  50, 40,  10, 9,   5,  4,   1}; 
    string result;

    for(int i=0; num!=0; i++){
        while(num >= value[i]){
            num -= value[i];
            result+=symbol[i];
        }
    }

    return result;
}


int main(int argc, char** argv)
{
    int num = 1234;
    if (argc>0){
        num = atoi(argv[1]);
    }    

    cout << num << " : " << intToRoman(num) << endl;
    return 0;
}

#include <string>
#include <unordered_map>
using std::string;

class Solution {
public:
    string intToRoman(int num) {
        std::map<int, string> map = {{1000, "M"}, {900, "CM"}, {500, "D"}, {400, "CD"}, {100, "C"}, 
                                     {90, "XC"}, {50, "L"}, {40, "XL"}, {10, "X"}, {9, "IX"}, {5, "V"}, {4, "IV"}, {1, "I"}};
        string ret;
        for (auto iter = map.rbegin(); iter != map.rend(); ++iter)
            while (num >= iter->first)
            {
                ret += map[iter->first];
                num -= iter->first;
            }
        return ret;
    }
};

/// Source : https://leetcode.com/problems/integer-to-roman/description/
/// Author : liuyubobobo
/// Time   : 2018-09-16

#include <iostream>
#include <cmath>

using namespace std;


/// Ad-Hoc
/// Time Complexity: O(1)
/// Space Complexity: O(1)
class Solution {
public:
    string intToRoman(int num) {

        string res = "";
        string one[] = {"I", "X", "C", "M", ""}, five[] = {"V", "L", "D", ""};
        for(int k = 3; k >= 0; k --){
            int b = (int)pow(10, k);
            if(num >= b){
                int x = num / b;
                res += rome(x, one[k], five[k], one[k + 1]);
                num %= b;
            }
        }
        return res;
    }

private:
    string rome(int x, string one, string five, string ten){
        if(x <= 3)
            return string(x, one[0]);
        else if(x == 4)
            return one + five;
        else if(x <= 8)
            return five + string(x - 5, one[0]);
        // x == 9
        return one + ten;
    }
};


int main() {

    return 0;
}