Given a roman numeral, convert it to an integer.

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

https://oj.leetcode.com/problems/roman-to-integer/

思路1：从前向后遍历罗马数字，如果某个数比前一个数小，则加上该数。反之，减去前一个数的两倍然后加上该数。

public class Solution {    public int romanToInt(String s) {        char[] symbol = { ‘I‘, ‘V‘, ‘X‘, ‘L‘, ‘C‘, ‘D‘, ‘M‘ };        int[] val = { 1, 5, 10, 50, 100, 500, 1000 };        Map<Character, Integer> map = new HashMap<Character, Integer>();        for (int i = 0; i < symbol.length; i++)            map.put(symbol[i], val[i]);        int len = s.length();        int res = 0;        res += map.get(s.charAt(0));        for (int i = 1; i < len; i++) {            int cur = map.get(s.charAt(i));            int pre = map.get(s.charAt(i - 1));            if (cur <= pre) {                res += cur;            } else {                res = res + cur - 2 * pre;            }        }        return res;    }    public static void main(String[] args) {        System.out.println(new Solution().romanToInt("MCMXC"));    }}

参考：

http://blog.csdn.net/wzy_1988/article/details/17057929