罗马数字

import java.util.*;

class Solution {
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 += 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;
}
}
}