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:
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I can be placed before V (5) and X (10) to make 4 and 9.
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X can be placed before L (50) and C (100) to make 40 and 90.
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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:
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1 <= s.length <= 15
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s contains only the characters ('I', 'V', 'X', 'L', 'C', 'D', 'M') .
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It is guaranteed that s is a valid roman numeral in the range [1, 3999] .