LeetCode 13 Roman to Integer(罗马数字转为整数)

int toNumber(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;
        }
        return 0;
 }

package leetcode_50;

/***
 * 
 * @author pengfei_zheng
 * 罗马数字转为整数
 */
public class Solution13 {
    public int romanToInt(String s) {
        int len = s.length();
        int ans = toNumber(s.charAt(len-1));
        for(int i=len-2;i>=0;i--){
            int last = toNumber(s.charAt(i+1));
            int first = toNumber(s.charAt(i));
            if(first>=last){//后面字符单位小于前面字符单位，加上对应数字
                ans+=first;
            }
            else//减去对应数字
                ans-=first;
        }
        return ans;
    }
    int toNumber(char ch) {//对应转换规则
        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;
        }
        return 0;
    }
}