[LeetCode]Integer to Roman

Given an integer, convert it to a roman numeral.

Input is guaranteed to be within the range from 1 to 3999.

思考：罗马数字有I,V,X,L,C,D,M。其中4,9左减，其他右加。

class Solution {

public:

    string intToRoman(int num) {

        // IMPORTANT: Please reset any member data you declared, as

        // the same Solution instance will be reused for each test case.

		if(num<1||num>3999) return NULL;

        const int integer[] = {1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1};

        const string roman[] = {"M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I"};

        string ret="";

		int i;

		for(i=0;i<13;i++)

		{

			while(num>=integer[i])

			{

				num-=integer[i];

				ret+=roman[i];			

			}

		}

		return ret;

    }

};