Roman to Integer

当前一位小于后一位的时候才是后一位减去前一位，并且这种位数只有一位

public class Solution {
    public int romanToInt(String s) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        int result = 0;
        if (s == null || s.length() == 0) {
             return result;
         }
        for (int i = 0; i < s.length(); i++) {
             if (i > 0 && cToI(s.charAt(i)) > cToI(s.charAt(i - 1))) {  
                 result += cToI(s.charAt(i)) - cToI(s.charAt(i - 1)) * 2;
             } else {
                 result += cToI(s.charAt(i));
            }
         }
         return result;
     }
     
     private static int cToI(char c) {
         switch (c) {
         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;
         default:
             return 0;
         }
    }
}