Int to Roman

阿拉伯数字转罗马数字（1~3999）

思路：

直接从个位数开始转起，分别用10,100,1000,10000取余数，不同的余数采用不同的解决办法，最后返回字符串

代码

class Solution {
public:
    string intToRoman(int num)
{
    int d = 10;
    int n = num;
    string rslt("");
    while (n > 0)
    {
        //给10取余数
        int single = n % 10;
        switch (single)
        {
        case 0:
            break;
        case 4:
            rslt += "IV" ; break;
        case 5:
            rslt += "V" ; break;    
        case 1: case 2:case 3:
        {
            int tmp = single;
            while (tmp > 0)
            {
                rslt += "I";
                    --tmp;
            }
            break;      
        }
        case 6:case 7: case 8:
        {
            int tmp = single;
            rslt += "V";
            while (tmp > 5)
            {
                rslt += "I";
                --tmp;
            }
            break;
        }
        case 9:
            rslt += "IX"; break;
        }
        //减去
        n = n - single;
        if (n == 0)
            return rslt;


        //给100取余数
        int decade = n % 100;
        switch (decade)
        {
        case 40:
            rslt = "XL"+rslt; break;
        case 50:
            rslt = "L" + rslt; break;
        case 0:
            break;
        case 10: case 20:case 30:
        {
            int tmp = decade;
            while (tmp >= 10)
            {
                rslt = "X" + rslt;
                    tmp -= 10;
            }
            break;
        }
        case 60:case 70: case 80:
        {
            int tmp = decade;
            string tmpRslt = "L";
            while (tmp > 50)
            {
                tmpRslt += "X";
                tmp -= 10;
            }
            rslt = tmpRslt + rslt;
            break;
        }
        case 90:
        {
            rslt = "XC" + rslt;
            break;

        }
        }
        //减去
        n = n - decade;
        if (n == 0)
            return rslt;
        //给1000取余数
        int hunderd = n % 1000;
        switch (hunderd)
        {
        case 0:
            break;
        case 400:
            rslt = "CD" + rslt; break;
        case 500:
            rslt = "D" +rslt; break;
        case 100: case 200:case 300:
        {
            int tmp = hunderd;
            while (tmp >= 100)
            {
                rslt = "C" + rslt;
                    tmp -= 100;
            }
            break;

        }
        case 600:case 700: case 800:
        {
            int tmp = hunderd;
            string tmpRslt = "D";
            while (tmp > 500)
            {
                tmpRslt += "C";
                tmp-=100;
            }
            rslt = tmpRslt + rslt;
            break;
        }
        case 900: 
        {
            rslt = "CM" + rslt;
            break;
        }
        }
        //减去
        n = n - hunderd;
        if (n == 0)
            return rslt;
        //给10000取余数
        int thousand = n % 10000;
        switch (thousand)
        {
        case 1000:
            rslt = "M" + rslt; break;
        case 2000:
            rslt = "MM" + rslt; break;
        case 3000:rslt = "MMM" + rslt; break;
        }
        n = n - thousand;
    }

    return rslt;

}
};