这是 integer 程序的罗马数字，但 output 不是我所期望的

Question

I expect 1994 as output, but i get 1014 when the input is MCMXCIV . Can you please give suggestions where my code went wrong. im a beginner to python, Thank you.

class Solution:
    def r2int(self,s):
        roman = {
            'I': 1,
            'V': 5,
            'X': 10,
            'L': 50,
            'C': 100,
            'D': 500,
            'M': 1000
        }
        s = s.replace('IV', 'IIII').replace('IX', 'V') #using replace function for exceptions
        s = s.replace('XL', 'XXX').replace('XC', 'V')
        s = s.replace('CD', 'V').replace('CM', 'V')
        integer = 0                                                #this is yet to become the final value
        for i in s:                                          #taking a character
            integer += roman[i]                                    #taking value from roman and adding to integer
        return integer                                             #final integer value
Solution().r2int('MCMXCIV')

Answer 1

There is a simpler approach. Let's map each numeral to its value.

roman = {
    'I': 1,
    'V': 5,
    'X': 10,
    'L': 50,
    'C': 100,
    'D': 500,
    'M': 1000
}

sample = 'MCMXCIV'

converted = [roman[digit] for digit in sample]

Now converted is [1000, 100, 1000, 10, 100, 1, 5] .

We could sum these, but that wouldn't account for things like IV . But if we negate any that are followed by a larger numeral, then we could sum them. We'll consider everything but the final digit.

for i in range(len(converted) - 1):
    if converted[i] < converted[i + 1]:
        converted[i] *= -1

Now converted is [1000, -100, 1000, -10, 100, -1, 5] .

And if we sum those numbers with sum(converted) , we get 1994 .

Answer 2

You replace some of the Roman numerals wrong. For example, IX (which is 9) is not V (which is 5), XC (which is 90) is not V (5), etc. Replace:

s = s.replace('IV', 'IIII').replace('IX', 'V') #using replace function for exceptions
s = s.replace('XL', 'XXX').replace('XC', 'V')
s = s.replace('CD', 'V').replace('CM', 'V')

with

s = s.replace('IV', 'IIII').replace('IX', 'VIIII') #using replace function for exceptions
s = s.replace('XL', 'XXXX').replace('XC', 'LXXXX')
s = s.replace('CD', 'CCCC').replace('CM', 'DCCCC')

then the code works as expected.