[Leetcode] integer to Roman and Roman to integer

[Question]

Given a roman numeral, convert it to an integer. Or, given an integer, convert it to a roman numeral.

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

[Roman numerals]

1 ~ 9: {"I", "II", "III", "IV", "V", "Vi", "VII", "VIII", "IX "};

10 ~ 90: {"X", "XX", "XXX", "XL", "L", "lx", "LXX", "LXXX", "XC "};

100 ~ 900: {"C", "cc", "CCC", "cd", "D", "DC", "DCC", "DCCC", "cm "};

1000 ~ 3000: {"M", "mm", "mmm "}.

[Roman numerals to Integers]

class Solution {public:    int romanToInt(string s) {        int ret = toNumber(s[0]);        for (int i = 1; i < s.length(); i++) {            if (toNumber(s[i - 1]) < toNumber(s[i])) {                ret += toNumber(s[i]) - 2 * toNumber(s[i - 1]);            } else {                ret += toNumber(s[i]);            }        }        return ret;    }        int toNumber(char ch) {        switch (ch) {            case 'I': return 1;            case 'V': return 5;            case 'X': return 10;            case 'L': return 50;            case 'C': return 100;            case 'D': return 500;            case 'M': return 1000;        }        return 0;    }};

[Integer to Roman numerals]

public class Solution {    public String intToRoman(int num) {        String[][] roman = {            {"", "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX"},            {"", "X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC"},            {"", "C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM"},            {"", "M", "MM", "MMM"}        };                String ret = "";        int digit = 0;        while (num != 0) {            int remain = num % 10;            ret = roman[digit][remain] + ret;            digit++;            num /= 10;        }                return ret;    }}

[Leetcode] integer to Roman and Roman to integer