文章标题

12. Integer to Roman

Given an integer, convert it to a roman numeral.

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

由上图可知，数字都可由1，4，5，9，10，40，50，90，100，400，500，900，1000构成；

string intToRoman(int num) {
    string symbal[] = { "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 };

    string str = "";
    for (int i = 0; num != 0; i++){
        while (num >= value[i]){
            str += symbal[i];
            num -= value[i];
        }
    }
    return str;
}

13. Roman to Integer

Given a roman numeral, convert it to an integer.

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

int romanToInt(string s) {
    map<char, int> res = { { 'I', 1 }, { 'V', 5 }, { 'X', 10 }, { 'L', 50 },
                           { 'C', 100 }, { 'D', 500 }, { 'M', 1000 } };

    int sum = res[s[0]];
    for (int i = 1; i < s.size(); i++){
        if (res[s[i - 1]] < res[s[i]])
            sum += res[s[i]] - 2 * res[s[i - 1]];
        else
            sum += res[s[i]];
    }
    return sum;
}