題目 : 13. Roman to Integer
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, 2
is written as II
in Roman numeral, just two ones added together. 12
is written as XII
, which is simply X + II
. The number 27
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.
Example 1:
Input: s = "III"
Output: 3
Explanation: III = 3.
Example 2:
Input: s = "LVIII"
Output: 58
Explanation: L = 50, V= 5, III = 3.
Example 3:
Input: s = "MCMXCIV"
Output: 1994
Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.
1.
class Solution:
def romanToInt(self, s: str) -> int:
# 先建立羅馬數字的字典roman
roman = {
"I": 1,
"V": 5,
"X": 10,
"L": 50,
"C": 100,
"D": 500,
"M": 1000
}
#字串是從最後面開始看,所以建立一個 s 的倒序字串 target,方便計算數字的總和(total)
target = s[::-1]
total = 0
if len(target) == 1: # 如果長度是1就可以直接回傳該羅馬字母所代表的數字
total = roman[s]
return total
i = 0
index = len(target)
while(i<len(s)):
#如果目前的羅馬數字>下一個羅馬字母的值,
#就可以將下一個羅馬字母的值減去目前的羅馬數字,再將i+2
if i+1 < index and roman[target[i]] > roman[target[i+1]]:
total = total + roman[target[i]] - roman[target[i+1]]
i = i+2
else:
# 若是其他的狀況則是將目前羅馬字母的值加到total
total = total + roman[target[i]]
i = i+1
return total