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Roman to Integer

MathString

EasyLeetCode #13

15 min

Problem Statement

Given a roman numeral, convert it to an integer.

Example

Example 1:

Input: s = "LVIII"

LVIII58

Output: 58

Explanation: L = 50, V = 5, III = 3.

Solution (Left-to-Right Pass)

A simple and effective way to convert a Roman numeral to an integer is to process the string from left to right. The key is to handle the cases where a smaller value precedes a larger one (like IV for 4 or IX for 9).

Algorithm Steps

Create a map to store the integer values of each Roman symbol.
Initialize a result variable to 0.
Iterate through the Roman numeral string from left to right.
For each symbol, check if the next symbol has a larger value.
If it does, subtract the current symbol's value from the result.
Otherwise, add the current symbol's value to the result.
After the loop, the result will hold the final integer value.

Input (Roman):

Result: 0

Start with Roman numeral "LVIII" and a result of 0.

Roman to Integer Solution


class Solution:
    def romanToInt(self, s: str) -> int:
        m = {
            'I': 1,
            'V': 5,
            'X': 10,
            'L': 50,
            'C': 100,
            'D': 500,
            'M': 1000
        }
        
        ans = 0
        
        for i in range(len(s)):
            if i < len(s) - 1 and m[s[i]] < m[s[i+1]]:
                ans -= m[s[i]]
            else:
                ans += m[s[i]]
        
        return ans