Roman to Integer
description:
Given a roman numeral, convert it to an integer. Input is guaranteed to be within the range from 1 to 3999.
thinking:
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”}.
solution：
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; } };
