Python将罗马数字转换为整数

Question

我尝试了以下从罗马到整数的python3代码

代码一目了然运行良好。但是，当我输入X、V或与X和V值相关时，出现了某些问题

例如：当我尝试V时，代码不起作用，但IV显示正确的值

我的代码：

class Solution(object):
   def romanToInt(self, s):
      """
      :type s: str
      :rtype: int
      """
      roman = {'I':1,'V':5,'X':10,'L':50,'C':100,'D':500,'M':1000,'IV':4,'IX':9,'XL':40,'XC':90,'CD':400,'CM':900}
      i = 0
      num = 0
      while i < len(s):
         if i+1<len(s) and s[i:i+2] in roman:
            num+=roman[s[i:i+2]]
            i+=2
         else:
            #print(i)
            num+=roman[s[i]]
            i+=1
      return num
ob1 = Solution()

message = str(input("Please enter your roman number: "))
if message <= ("MMMCMXCIX"):
   print (ob1.romanToInt(message))
else:
    print ("Try again")

我设置了一个条件，如果输入的罗马数字等于或小于MMMCMXCIX，它将打印罗马数字；否则它将打印Try again

问题是当我输入X、V或与X和V相关的值时，输出显示Try again

请帮助我理解我哪里出了错

Answer 1

正如注释中提到的，问题是因为比较了字符串而不是首先转换为int，然后进行比较

您可以尝试的其他方法是：

def romanToInt(s):
  d = {'m': 1000, 'd': 500, 'c': 100, 'l': 50, 'x': 10, 'v': 5, 'i': 1}
  n = [d[i] for i in s.lower() if i in d]
  return sum([i if i>=n[min(j+1, len(n)-1)] else -i for j,i in enumerate(n)])

print(romanToInt('X')) # 10
print(romanToInt('V')) # 5
print(romanToInt('IV')) # 4
print(romanToInt('XV')) # 15

在我看来，两者都更像Python

Answer 2

最后，它只是一个数字的加法，你只需要弄清楚它们是否需要被解释为正数或负数：

roman = {'I':1,'V':5,'X':10,'L':50,'C':100,'D':500,'M':1000,'IV':4,'IX':9,'XL':40,'XC':90,'CD':400,'CM':900}

def roman2Dec(inp):
    inpNum = [roman[x] for x in inp]
    return sum([-x if i < len(inpNum)-1 and x < inpNum[i+1] else x for i, x in enumerate(inpNum)])

for nums in [('IX', 9), ('XL', 40), ('LXI', 61), ('MMMCMXCIX', 3999)]:
    result = roman2Dec(nums[0])
    print result == nums[1]

输出：

True
True
True
True

Answer 3

这是因为您要比较字符串，而不是首先将罗马字符转换为int而不是check

class Solution(object):
   def romanToInt(self, s):
      """
      :type s: str
      :rtype: int
      """
      roman = {'I':1,'V':5,'X':10,'L':50,'C':100,'D':500,'M':1000,'IV':4,'IX':9,'XL':40,'XC':90,'CD':400,'CM':900}
      i = 0
      num = 0
      while i < len(s):
         if i+1<len(s) and s[i:i+2] in roman:
            num+=roman[s[i:i+2]]
            i+=2
         else:
            #print(i)
            num+=roman[s[i]]
            i+=1
      return num
ob1 = Solution()

message = str(input("Please enter your roman number: "))
# converting to integer than comparing the value of "MMMCMXCIX"
if ob1.romanToInt(message) <= 8999:
   print (ob1.romanToInt(message))
else:
    print ("Try again")