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

给定一个罗马数字，将其转换成整数。
返回的结果要求在1到3999的范围内。
说明什么是 罗马数字?
https://en.wikipedia.org/wiki/Roman_numerals
https://zh.wikipedia.org/wiki/%E7%BD%97%E9%A9%AC%E6%95%B0%E5%AD%97
http://baike.baidu.com/view/42061.htm
样例IV
-> 4
XII
-> 12
XXI
-> 21
XCIX
-> 99

分析

运用hashmap

代码

public class Solution {
    /**
     * @param s Roman representation
     * @return an integer
     */
    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;
    }
}