贪心算法，先通过map将罗马字符和数字一一对应，进行有序排列，然后从最大的数字开始，进行数字到罗马字符的转换
class Solution {
public:
string intToRoman(int num) {
map<int, string> map = {{1, "I"},
{4, "IV"},
{5, "V"},
{9, "IX"},
{10, "X"},
{40, "XL"},
{50, "L"},
{90, "XC"},
{100, "C"},
{400, "CD"},
{500, "D"},
{900, "CM"},
{1000, "M"}};
auto reverse_iter = map.rbegin();
string res;
while (reverse_iter != map.rend()) {
if (num >= reverse_iter->first) {
num -= reverse_iter->first;
res += reverse_iter->second;
} else {
reverse_iter++;
}
}
return res;
}
};
