Integer to Roman.txt

problem：
Given an integer, convert it to a roman numeral.

Input is guaranteed to be within the range from 1 to 3999.
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solution：
这题的关键在于roman numeral的理解，基本元素组成有：
//'I' 1
//'V' 5
//'X' 10
//'L' 50
//'C' 100
//'D' 500
//'M' 1000
但还有一个习惯就是，比如IIII表示成IV，所以其实可以组成以下这些情况：
//"M","CM","D","CD","C","XC","L","XL","X","IX","V","IV","I"
//1000,900,500,400,100,90,50,40,10,9,5,4,1

void appendSymbol(string& res, int cot, char symbol[])
{
  if(cot == 0)
		return;
	else if(cot <= 3)
		res.append(cot, symbol[0]);
	else if(cot == 4)
	{
		res.append(1, symbol[0]);
		res.append(1, symbol[1]);
	}
	else if(cot <= 8)
	{
		res.append(1, symbol[1]);
		res.append(cot - 5, symbol[0]);
	}
	else //cot == 9
	{
		res.append(1, symbol[0]);
		res.append(1, symbol[2]);
	}
}

string intToRoman(int num)
{
  if(num <= 0)
		return NULL;
	char symbol[] = {'I', 'V', 'X', 'L', 'C', 'D', 'M'};
	string result;
	int scale = 1000;
	for(int i = 6; i >=0; i -= 2)
	{
		int n = num / scale;
		appendSymbol(result, n, symbol + i);
		num = num % scale;
		scale /= 10;
	}
	return result;
}