leetcode013-python 羅馬數字轉整數
阿新 • • 發佈：2019-01-09
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
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
Ican be placed beforeV(5) andX(10) to make 4 and 9.Xcan be placed beforeL(50) andC(100) to make 40 and 90.Ccan 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.
解題要點：
1.用字典轉換羅馬數字和阿拉伯數字；
2.對羅馬數字讀法的轉換，可以先依次讀入字串，遇到前面比後面小的情況在減去之前加上的就行；
class Solution:
def romanToInt(self, s):
"""
:type s: str
:rtype: int
"""
d = {'I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100, 'D': 500, 'M': 1000}
n = len(s)
ans = 0
for i in range(n):
if i<n and d[s[i]] > d[s[i-1]] and i > 0:
ans += d[s[i]] - 2*d[s[i-1]]
else:
ans += d[s[i]]
return ans