Convert Roman Number to Decimal (Integer) | Write Python Program to Convert Roman to Integer
In this tutorial, we will write the Python program to convert the Roman numbers into the integer. It is a popular problem was asked by the tech giant Amazon, Facebook in the interview. Let’s see the problem statement and implementation of the solution.
Problem Statement
A roman number is given as a string; the task is to convert the corresponding integer value. The symbols are given below for reference.
| Symbols | Values |
|---|---|
| I | 1 |
| IV | 4 |
| V | 5 |
| IX | 9 |
| X | 10 |
| XL | 40 |
| L | 50 |
| XC | 90 |
| C | 100 |
| CD | 400 |
| D | 500 |
| CM | 900 |
| M | 1000 |
Example 1:
Input:s = VI
Output: 6
Example 2:
Input: XOutput: 10XL is a Roman symbol which represents 40
Solution Approach
Algorithm
- First, split the Roman numeral string into roman symbols.
- We can the separate symbol now convert each symbol of Roman Numerals into the value it represents.
- Picking up a value starting from index 0.
- If the current value of the symbol is greater than or equal to the next symbol, then add this value to the returning total.
- Else subtract this value by adding the value of the next symbol to the running total.
Let’s implement the algorithm to the Python program.
Program
Output:
7
Explanation
In the above code, we define a rom_value() function which returns corresponding to the symbol. Next we define the romanTointeger() method which converts the value roman value to integer. In the romanToInteger() method,
- We have defined the res and i variable with 0.
- The while iterated till i is smaller than the length of the string.
- We converted the first character into an integer and stored it into n1. Then, use the condition to check the i+1th element smaller than the length of the string.
- If it returns true, it converts into an integer and is stored in n2.
- Compare n1 and n2; if n1 is greater than the n2, add it to the res and increase the ith value by one.
- If it returns false, then subtract the n2 to n1 and make the increment of 2 in i.
- If first if condition returns false add into the res and make increment to i
Complexity Analysis
Time Complexity: O(n), where n is the length of the string. Only one traversal of the string is required.
Space Complexity: O(1). As no extra space is required