Last Updated: 18 Dec, 2020
Roman Numeral To Integer
Easy
Asked in companies
You are given a string 's' that represents a Roman number. Convert the Roman number to an integer and return it.
Roman numerals are represented by seven different symbols: I, V, X, L, C, D, and M.
Table of values:
Symbol Value
I 1
V 5
X 10
L 50
C 100
D 500
M 1000
For example:
3 is written as III in Roman numeral, just three ones added together. 13 is written as XIII, which is simply X + III. The number 25 is written as XXV, which is XX + V
Input format:
The first line contains a string ‘roman’ representing the number's roman number representation.
Output Format
The only line contains a single integer denoting the integer value of the given roman number.
Note:
Do not print anything, just return an integer denoting the equivalent integer of the given roman number
It is guaranteed that the string input is one of the characters of I, V, X, L, C, D, M.
It is guaranteed that the integer value of the given roman number will not exceed 3999.
Approaches
The key idea is to follow the rules of roman numbers which are as follows:
- The roman digits I, X and C are repeated up to three times in succession to form the numbers.
- When a digit of lower value is written to the right or after a digit of higher value, the values of all the digits are added.
- When a digit of lower value is written to the left or before a digit of higher value, then the value of the lower digit is subtracted from the value of the digit of higher value.
- If we have to write the numbers beyond 10 we should write the number 10 or groups of number 10 and then number 1 or 5 as the case may be. Then these numbers are used to change to the corresponding Roman numerals.
Keeping the above example in mind, we can write the following recursive solution:
- We take a recursive approach to solve the problem.
- We make a hash map ‘conv’ which stores integer values of special roman numbers.
- Then, we take the first 2 characters and check if they are in the map, if yes we add their value and recursively call the rest of the string.
- If the first 2 characters are not there in the map, we add the value of 1 character and recursively call the rest of the string.
- The base case will be once we have a string of size 1 or an empty string. In that case, we return 0.
The key idea is to follow the rules of roman numbers which are as follows:
- The roman digits I, X and C are repeated up to three times in succession to form the numbers.
- When a digit of lower value is written to the right or after a digit of higher value, the values of all the digits are added.
- When a digit of lower value is written to the left or before a digit of higher value, then the value of the lower digit is subtracted from the value of the digit of higher value.
- If we have to write the numbers beyond 10 we should write the number 10 or groups of number 10 and then number 1 or 5 as the case may be. Then these numbers are used to change to the corresponding Roman numerals.
Keeping the above example in mind, we can proceed in the following manner:
- We take a simple iterative approach to solve the problem.
- First, we define a function ‘romanToInt’ which takes a character and returns its integer representation.
- We make a variable ‘count’ to store the answer.
- Then, we simply traverse through the string, and if the current character value is more than the next character value we follow rule 2 and add the values.
- If the current character is less than the value of the next character, we subtract the value of the current character from the value of the next character.
- Finally, we return the variable ‘count’.