利用等价换算法将罗马数转为十进制数

class Solution:
    def romanToInt(self, s: str) -> int:
        roman_map={'I':1,'V':5,'X':10,'L':50,'C':100,'D':500,'M':1000}
        before_val,count=roman_map[s[0]],0
        for c in s:
            val=roman_map[c]
            if val<=before_val:
                count+=val
            else:
                count=count-val+2*(val-before_val)
            before_val=val
        return count

解题思路