Solution for interview question: Roman to Integer

1. Understanding the Problem

You are given a Roman numeral, and you need to convert it to an integer.
Roman numerals are made up of symbols (I, V, X, L, C, D, M) with respective values.
The numeral can range from 1 to 3999, and subtraction cases (like IV for 4) must be handled.

2. List Roman Numerals and Values

Roman numerals are represented by seven different symbols with specific values:

Symbol    Value 
 I         1
 V         5
 X         10
 L         50
 C         100
 D         500
 M         1000

Subtraction cases include:
- I before V (5) and X (10) to make 4 and 9.
- X before L (50) and C (100) to make 40 and 90.
- C before D (500) and M (1000) to make 400 and 900.

3. Create a Mapping for Roman Numerals

Use a dictionary to map Roman numeral symbols to their corresponding integer values.
This will allow for constant-time lookups during conversion.

def roman_to_integer(s: str) -> int:
    roman_map = {'I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100, 'D': 500, 'M': 1000}
    return 0

4. Iterate Through the String

To process the Roman numeral, iterate through the string from left to right.
For each character, look up its corresponding value using the dictionary.

def roman_to_integer(s: str) -> int:
    roman_map = {'I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100, 'D': 500, 'M': 1000}
    total = 0
    for char in s:
        value = roman_map[char]
    return total

5. Handle Subtraction Cases

Roman numerals use subtraction in specific cases (like IV = 4).
If a smaller value comes before a larger one, subtract the smaller value instead of adding it.

def roman_to_integer(s: str) -> int:
    roman_map = {'I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100, 'D': 500, 'M': 1000}
    total = 0
    prev_value = 0
    for char in s:
        value = roman_map[char]
        if value > prev_value:
            total += value - 2 * prev_value  # Subtract twice the previous value
        else:
            total += value
        prev_value = value  # Update the previous value
    return total

6. Return the Final Sum

After processing all characters in the Roman numeral string, return the accumulated total value, which represents the integer conversion.

def roman_to_integer(s: str) -> int:
    roman_map = {'I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100, 'D': 500, 'M': 1000}
    total = 0
    prev_value = 0
    for char in s:
        value = roman_map[char]
        if value > prev_value:
            total += value - 2 * prev_value
        else:
            total += value
        prev_value = value
    return total

7. Handle Edge Cases

Make sure that input Roman numerals are valid and within the range (1-3999).
Since the problem guarantees this, we don't need extra validation, but this could be added in a more general implementation.