動機
水
Problem
Roman numerals are represented by seven different symbols: I
, V
, X
, L
, C
, D
and M
.
Symbol ValueI 1V 5X 10L 50C 100D 500M 1000
For example, 2
is written as II
in Roman numeral, just two one's 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 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.
Example 1:
Input: s = IIIOutput: 3
Example 2:
Input: s = IVOutput: 4
Example 3:
Input: s = IXOutput: 9
Example 4:
Input: s = LVIIIOutput: 58Explanation: L = 50, V= 5, III = 3.
Example 5:
Input: s = MCMXCIVOutput: 1994Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.
Constraints:
1 <= s.length <= 15
s
contains only the characters('I', 'V', 'X', 'L', 'C', 'D', 'M')
.- It is guaranteed that
s
is a valid roman numeral in the range[1, 3999]
.
Sol
class Solution:
def romanToInt(self, s: str) -> int:
tbl = {"I":1 ,"V":5 ,"X":10 ,"L": 50 , "C": 100, "D":500, "M":1000}
tbl2 = {"IV":4 ,"IX":9 ,"XL": 40 , "XC": 90, "CD":400, "CM":900}
ret,i = 0,0
while i < len(s):
if s[i:i+2] in tbl2:
ret += tbl2[s[i:i+2]]
i += 2
else:
ret += tbl[s[i]]
i += 1
return ret