LeetCode Challenge 13: Roman to Integer - JavaScript Solution 🚀

Top Interview 150

Converting Roman numerals to integers involves understanding both their additive and subtractive notation rules. Let’s break down LeetCode 13: Roman to Integer and solve it step by step.

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🚀 Problem Description

Roman numerals are represented by seven symbols, each with a fixed value.

• Subtractive Rule: When a smaller numeral appears before a larger one, subtract the smaller numeral.

Given a Roman numeral string, return its integer equivalent.

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💡 Examples

Example 1

Input: s = "III"  
Output: 3  
Explanation: III = 3 (1 + 1 + 1).

Example 2

Input: s = "LVIII"  
Output: 58  
Explanation: L = 50, V = 5, III = 3.

Example 3

Input: s = "MCMXCIV"  
Output: 1994  
Explanation: M = 1000, CM = 900, XC = 90, IV = 4.  
             1994 = 1000 + 900 + 90 + 4.

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🏆 JavaScript Solution

To solve this problem, we use a mapping dictionary for Roman symbols and traverse the string to calculate the integer.

Implementation

var romanToInt = function(s) {
    const romanMap = {
        'I': 1,
        'V': 5,
        'X': 10,
        'L': 50,
        'C': 100,
        'D': 500,
        'M': 1000
    };

    let total = 0;

    for (let i = 0; i < s.length; i++) {
        const current = romanMap[s[i]];
        const next = romanMap[s[i + 1]];

        if (next && current < next) {
            total -= current;
        } else {
            total += current;
        }
    }

    return total;
};

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🔍 How It Works

1. Map Roman Symbols: Use a dictionary to map Roman symbols to their values.
2. Traverse the String: For each character:
   • Add the value to the total if the current numeral is greater than or equal to the next.
   • Subtract the value if the current numeral is smaller than the next (subtractive rule).
3. Return the Total: After traversing the string, total holds the integer equivalent.

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🔑 Complexity Analysis

• > Time Complexity: O(n), where n is the length of the string. We traverse the string once.
• > Space Complexity: O(1), as the mapping dictionary size is constant.

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📋 Dry Run
Input: s = "MCMXCIV"

Output: 1994

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✨ Pro Tips for Interviews

1. Clarify constraints: Confirm that the Roman numeral input will always be valid (as per problem assumptions).
2. Highlight efficiency: Emphasize O(n) time complexity and how the subtractive rule is handled efficiently.
3. Edge cases:
   • Smallest numeral ("I" → 1).
   • Mixed additive and subtractive cases ("XIV" → 14).

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📚 Learn More

Check out the full explanation and code walkthrough on my Dev.to post:
👉 Trapping Rain Water - JavaScript Solution

What’s your approach to solving this problem? Let’s discuss! 🚀

JavaScript #LeetCode #CodingInterview #ProblemSolving

Comments

[Rahul Kumar Barnwal]

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