LeetCode13题

import java.util.*;


public class Solution {
    /**
     * 
     * @param s string字符串 
     * @return int整型
     */
    public int romanToInt (String s) {
        // write code here
        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 += 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;
        }
    }
}