LeetCode

题目：

Given a roman numeral, convert it to an integer.
Input is guaranteed to be within the range from 1 to 3999.

思路：

把关键数值对应起来，然后n-1位扫到第0位。

package manipulation;

import java.util.HashMap;

public class RomanToInteger {

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

        int res = map.get(s.charAt(len - 1));
        for (int i = len - 2; i >= 0; --i) {
            if (map.get(s.charAt(i + 1)) > map.get(s.charAt(i)))
                res -= map.get(s.charAt(i));
            else
                res += map.get(s.charAt(i));
        }
        
        return res;
    }
    
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        RomanToInteger r = new RomanToInteger();
        System.out.println(r.romanToInt("MCM"));
    }

}