LeetCode12——Roman to Integer

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题目链接

Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.

Symbol       Value
I             1
V             5
X             10
L             50
C             100
D             500
M             1000

For example, two is written as II in Roman numeral, just two one's added together. Twelve is written as, XII, which is simply X + II. The number twenty seven is written as XXVII, which is XX + V + II.

Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is not IIII. Instead, the number four is written as IV. Because the one is before the five we subtract it making four. The same principle applies to the number nine, which is written as IX. There are six instances where subtraction is used:

• I can be placed before V (5) and X (10) to make 4 and 9. 
• X can be placed before L (50) and C (100) to make 40 and 90. 
• C can be placed before D (500) and M (1000) to make 400 and 900.

Given a roman numeral, convert it to an integer. Input is guaranteed to be within the range from 1 to 3999.

Example 1:

Input: "III"
Output: 3

Example 2:

Input: "IV"
Output: 4

Example 3:

Input: "IX"
Output: 9

Example 4:

Input: "LVIII"
Output: 58
Explanation: L = 50, V= 5, III = 3.

Example 5:

Input: "MCMXCIV"
Output: 1994
Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.

代码

class Solution:
    def romanToInt(self, s: 'str') -> 'int':
        res = 0
        i = 0
        while i < len(s):
            special = s[i:i+2]
            routine = s[i]

            if special == "IV":
                res = res + 4
                i = i + 2
            elif special == "XL":
                res = res + 40
                i = i + 2
            elif special == "CD":
                res = res + 400
                i = i + 2
            elif special == "IX":
                res = res + 9
                i = i + 2
            elif special == "XC":
                res = res + 90
                i = i + 2
            elif special == "CM":
                res = res + 900
                i = i + 2
            elif routine == "I":
                res = res + 1
                i = i + 1
            elif routine == "V":
                res = res + 5
                i = i + 1
            elif routine == "X":
                res = res + 10
                i = i + 1
            elif routine == "L":
                res = res + 50
                i = i + 1
            elif routine == "C":
                res = res + 100
                i = i + 1
            elif routine == "D":
                res = res + 500
                i = i + 1
            elif routine == "M":
                res = res + 1000
                i = i + 1


        return res

结果

Runtime: 124 ms, faster than 81.26% of Python3 online submissions for Roman to Integer.
Memory Usage: 12.4 MB, less than 98.70% of Python3 online submissions for Roman to Integer

这个其实和LeetCode12差不多的。只要想好判断语句，就OK了。