leetcode/problems/0013-py/main.py at main · emfomy/leetcode · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
# Source: https://leetcode.com/problems/roman-to-integer
# Title: Roman to Integer
# Difficulty: Easy
# Author: Mu Yang <http://muyang.pro>

################################################################################################################################
# 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.
# ```
#
# **Constraints:**
#
# - `1 <= s.length <= 15`
# - `s` contains onlythe characters `('I', 'V', 'X', 'L', 'C', 'D', 'M')`.
# - It is **guaranteed**that `s` is a valid roman numeral in the range `[1, 3999]`.
#
################################################################################################################################


class Solution:
    def romanToInt(self, s: str) -> int:
        romans = {
            "I": 1,
            "V": 5,
            "X": 10,
            "L": 50,
            "C": 100,
            "D": 500,
            "M": 1000,
        }

        ans = 0
        prev = 0
        for ch in reversed(s):
            curr = romans[ch]
            if curr >= prev:
                ans += curr
            else:
                ans -= curr
            prev = curr

        return ans