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 beforeV
(5) andX
(10) to make 4 and 9.X
can be placed beforeL
(50) andC
(100) to make 40 and 90.C
can be placed beforeD
(500) andM
(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: C = 100, L = 50, XXX = 30 and III = 3.
Example 5:
Input: "MCMXCIV" Output: 1994 Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.
思路:因为这道题4和9的特殊性,于是我就想到了先把特殊的字符先替换掉的操作,于是剩下的罗马数字都是单个字符的了。
class Solution: def romanToInt(self, s): """ :type s: str :rtype: int """ data = {'I':1, 'V':5, 'X':10, 'L':50, 'C':100, 'D':500, 'M':1000} result = 0 if 'CD' in s: result += 400 s = s.replace("CD", "") elif 'CM' in s: result += 900 s = s.replace("CM", "") if 'XL' in s: result += 40 s = s.replace("XL", "") elif 'XC' in s: result += 90 s = s.replace("XC", "") if 'IV' in s: result += 4 s = s.replace("IV", "") elif 'IX' in s: result += 9 s = s.replace("IX", "") for i in set(s): result += data[i]*(s.count(i)) return result
Beat 98
总结:遇到难处理的特殊情况,不如把特殊情况给消除了,剩下的就是正常情况。