[LeetCode] Roman to Integer, leetcoderoman

[LeetCode] Roman to Integer, leetcoderoman

Given a roman numeral, convert it to an integer.

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

This question mainly involves figuring out the algorithm for turning Roman into Integer.

Remember that if a number is smaller than the previous one, it will be used as a plus number, and vice versa, it will be used as a reduction. (Eg: IV = 4, XLV = 45, XX = 20)

Therefore, we can start from the end of the team and slowly determine whether a number should be + or -.

The Code is as follows .~

public class Solution {    public int romanToInt(String s) {        if(s==null||s.length()==0){            return 0;        }        HashMap<Character,Integer> hash=new HashMap<Character,Integer>();        hash.put('I',1);        hash.put('V',5);        hash.put('X',10);        hash.put('L',50);        hash.put('C',100);        hash.put('D',500);        hash.put('M',1000);        int len=s.length();        int result=hash.get(s.charAt(len-1));        int compare=result;        for(int i=len-2;i>=0;i--){            int curr=hash.get(s.charAt(i));            if(curr>=compare){                result=result+curr;            }else{                result=result-curr;            }            compare=curr;        }        return result;    }}