[Leetcode questions and Notes] Roman to integer

Given a roman numeral, convert it to an integer.

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

 

Question: Conversion Method: scan the Rome character from left to right. If the number corresponding to the current character is smaller than the previous one, add the number directly; otherwise, add this number and subtract twice the previous number, and then update the previous number. Use a hashmap to store the correspondence between Roman characters and numbers.

See http://www.cnblogs.com/sunshineatnoon/p/3856057.html

For example, the Rome digital dcxix: 500 + 100 + 10 + 1 + 10-2 = 619

The Code is as follows:

 1 public class Solution { 2     public int romanToInt(String s) { 3         if(s == null || s.length() == 0) 4             return 0; 5          6         HashMap<Character, Integer> map= new HashMap<Character,Integer>(); 7         map.put(‘I‘, 1); 8         map.put(‘V‘, 5); 9         map.put(‘X‘, 10);10         map.put(‘L‘, 50);11         map.put(‘C‘, 100);12         map.put(‘D‘, 500);13         map.put(‘M‘, 1000);14         15         int length = s.length();16         int result = map.get(s.charAt(0));17         int last = result;18         19         for(int i = 1;i < length;i++){20             int temp = map.get(s.charAt(i));21             if(temp <= last)22                 result += temp;23             else24                 result = result + temp - 2*last;25             last = temp;26         }27         28         return result;29     }30 }