【leetcode】Integer to Roman

class Solution {
public:
    string intToRoman(int num) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function    
        string res;
        
        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};
        
	    int i = 0;
	    while(num != 0){
		    if(num >= value[i]){    // minus largest number
			    num -= value[i];
		    	res += symbol[i];
		    } else {
    	        i++;   
		    }
	    }

	    return res;
    }
};

class Solution {
public:
    string intToRoman(int num) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function    
        char symbol[7] = {'I', 'V', 'X', 'L', 'C', 'D', 'M'};
        string res = "";
        
        int scale = 1000;
        for (int i = 6; i >= 0; i -= 2)
        {
            int digit = num / scale;
            num2roman(digit, res, symbol + i);
            num %= scale;
            scale /= 10;
        }
        
        return res;
    }
    
    void num2roman(int num, string& res, char symbols[])
    {
        if (num == 0)
            return;
        if (num <= 3)
            res.append(num, symbols[0]);
        else if (num == 4)
        {
            res.append(1, symbols[0]);
            res.append(1, symbols[1]);
        }
        else if (num <= 8)
        {
            res.append(1, symbols[1]);
            res.append(num - 5, symbols[0]);
        }
        else
        {
            res.append(1, symbols[0]);
            res.append(1, symbols[2]);
        }
    }
};