---
title: "13. Roman to Integer"
tags: LeetCode, Top100
---
#13 Roman to Integer
==
題目描述
--
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 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 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 an integer, convert it to a roman numeral.

Example 1:
--
>Input: s = "III"
Output: 3

Example 2:
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>Input: s = "LVIII"
Output: 58
Explanation: L = 50, V= 5, III = 3.

解題思維
--
建立好dict，從小到大逐一檢查這個數有沒有小於上一個數字，有就撿到。

BruteForce
--

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

        res, pre = 0, 0

        for i in s[::-1]:
            n = values[i]
            if n >= pre:
                res += n
            else:
                res -= n
            pre = n
        return res