Roman to Integer

Roman to Integer is a Easy Data Structures and Algorithms interview problem you can solve, run and submit on Thita.ai. It belongs to the String Manipulation Patterns pattern, in the Integer and Roman Conversion subpattern.

Problem statement

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 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].

Topics and companies

Topics: Hash Table, Math, String.

Reported in interviews at Amazon, Roblox, Microsoft, Adobe, Facebook, LinkedIn, Google, Apple, Uber, Qualtrics, Oracle, eBay.

How to practise Roman to Integer on Thita.ai

Starter code is provided in C, C#, C++, Go, Java, JavaScript and Python. Your solution runs against 5 test cases for this problem, with the AI coach available for a hint when you are stuck rather than a finished answer. The reference solution runs in O(n) time and O(1) space.

Open Roman to Integer in the code editor, or read the Roman to Integer editorial for a worked solution with its approach and complexity analysis.

Where Roman to Integer sits in the DSA pattern sheet

Problems related to Roman to Integer

Other problems that use the same Integer and Roman Conversion and String Manipulation Patterns techniques:

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