13. 羅馬數字轉整數

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

一言蔽之，把一個小值放在大值的左邊，就是做減法，否則為加法。

public class Solution {
    public static void main(String[] args) {
        Solution solution=new Solution();
     String s="IV";
     int a=solution.romanToInt(s);
        System.out.println("a = " + a);
    }

    public int romanToInt(String s) {
        int sum = 0;
        int preNum = getValue(s.charAt(0));
        for(int i = 1;i < s.length(); i ++) {
            int num = getValue(s.charAt(i));
            if(preNum < num) sum -= preNum;
            else sum += preNum;
            preNum = num;
        }

        sum =sum + preNum;
        return sum;
    }

    private int getValue(char ch) {
        switch(ch) {
            case 'I': return 1;
            case 'V': return 5;
            case 'X': return 10;
            case 'L': return 50;
            case 'C': return 100;
            case 'D': return 500;
            case 'M': return 1000;
            default: return 0;
        }
    }



}