Roman to Integer

Easy

Given a Roman numeral string, convert it to an integer. Roman numerals are represented by: I=1, V=5, X=10, L=50, C=100, D=500, M=1000. When a smaller numeral appears before a larger one, subtract it.

Examples

Input	Output
s = "III"	3
s = "MCMXCIV"	1994

Python Solution

def roman_to_int(s: str) -> int:
    values = {"I": 1, "V": 5, "X": 10, "L": 50, "C": 100, "D": 500, "M": 1000}
    total = 0
    prev = 0
    for c in reversed(s):
        v = values[c]
        total += v if v >= prev else -v
        prev = v
    return total

JavaScript Solution

function romanToInt(s) {
  const values = { I: 1, V: 5, X: 10, L: 50, C: 100, D: 500, M: 1000 };
  let total = 0, prev = 0;
  for (let i = s.length - 1; i >= 0; i--) {
    const v = values[s[i]];
    total += v >= prev ? v : -v;
    prev = v;
  }
  return total;
}

Step-by-Step Explanation

Process from right to left. If current value < previous, subtract; else add.
This handles cases like IV (4) and IX (9) correctly.

Complexity Analysis

Time	O(n)
Space	O(1)

Related Tools

Regex Tester

All Problems

Two Sum Reverse a String Palindrome Check FizzBuzz Binary Search Reverse Linked List Merge Two Sorted Arrays Valid Parentheses Maximum Subarray (Kadane's Algorithm)Remove Duplicates from Sorted Array Nth Fibonacci Number Valid Anagram First Unique Character Climbing Stairs Best Time to Buy and Sell Stock Contains Duplicate Move Zeroes Intersection of Two Arrays Longest Common Prefix