13. Roman to Integer【leetcode】

Roman to Integer

Given a roman numeral, convert it to an integer.

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

 public class Solution {
      public int romanToInt(String s) {
         if (s == null || s.length()==0) {
                 return 0;
         }
         Map<Character, Integer> m = new HashMap<Character, Integer>();
         m.put('I', 1);
         m.put('V', 5);
         m.put('X', 10);
         m.put('L', 50);
         m.put('C', 100);
         m.put('D', 500);
         m.put('M', 1000);

         int length = s.length();
         int result = m.get(s.charAt(length - 1));
         for (int i = length - 2; i >= 0; i--) {
             if (m.get(s.charAt(i + 1)) <= m.get(s.charAt(i))) {
                 result += m.get(s.charAt(i));
             } else {
                 result -= m.get(s.charAt(i));
             }
         }
         return result;
     }
 }

 // 方法二
 public class Solution {
     /**
      * @param s Roman representation
      * @return an integer
      */
     public int romanToInt(String s) {
         // Write your code here
         int ans;
         char[] sc = s.toCharArray();
         ans = toInt(sc[0]);                        //0 special
         for (int i = 1; i < s.length(); i++) {
             ans += toInt(sc[i]);
             if (toInt(sc[i - 1]) < toInt(sc[i])) {
                 ans -= toInt(sc[i - 1]) * 2;
             }
         }
         return ans;
     }

     int toInt(char s) {
         switch(s) {
             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;
     }
 }