Top Interview 150

Converting integers to Roman numerals is a fun problem involving string manipulation and careful application of Roman numeral rules. Let’s explore LeetCode 12: Integer to Roman, break down the steps, and implement the solution in JavaScript.

🚀 Problem Description

You are given an integer num (1 ≤ num ≤ 3999).
Return its Roman numeral representation.

Roman numerals follow specific rules:

• Symbols: I (1), V (5), X (10), L (50), C (100), D (500), M (1000).
• Use subtractive notation for 4, 9, 40, 90, 400, 900.

💡 Examples

Example 1

Input: num = 3749 Output: "MMMDCCXLIX" Explanation: - 3000 → `MMM` - 700 → `DCC` - 40 → `XL` - 9 → `IX` 

Example 2

Input: num = 58 Output: "LVIII" Explanation: - 50 → `L` - 8 → `VIII` 

Example 3

Input: num = 1994 Output: "MCMXCIV" Explanation: - 1000 → `M` - 900 → `CM` - 90 → `XC` - 4 → `IV` 

🏆 JavaScript Solution

To solve this problem, we’ll use a greedy approach:

• Start with the largest Roman numeral.
• Subtract its value from the number while appending the numeral to the result.
• Repeat until the number becomes zero.

Implementation

var intToRoman = function(num) { const romanMap = [ { value: 1000, symbol: 'M' }, { value: 900, symbol: 'CM' }, { value: 500, symbol: 'D' }, { value: 400, symbol: 'CD' }, { value: 100, symbol: 'C' }, { value: 90, symbol: 'XC' }, { value: 50, symbol: 'L' }, { value: 40, symbol: 'XL' }, { value: 10, symbol: 'X' }, { value: 9, symbol: 'IX' }, { value: 5, symbol: 'V' }, { value: 4, symbol: 'IV' }, { value: 1, symbol: 'I' }, ]; let result = ''; for (const { value, symbol } of romanMap) { while (num >= value) { result += symbol; num -= value; } } return result; }; 

🔍 How It Works

1. Roman Map:

   • Create an ordered list of Roman numeral values and their symbols.
   • Include subtractive notations (CM, XC, etc.) in the map.

2. Iterate Through the Map:

   • For each numeral, append it to the result while subtracting its value from num until num is less than the numeral’s value.

3. Return the Result:

   • After processing all numerals, the result contains the Roman numeral string.

🔑 Complexity Analysis

• > Time Complexity: O(1), because the number of Roman numeral symbols is constant (13). The loop runs a fixed number of iterations regardless of input size.
• > Space Complexity: O(1), as we only use a string to build the result.

📋 Dry Run

Input: num = 1994

Output: "MCMXCIV"

✨ Pro Tips for Interviews

1. Use a Roman map: Predefining values simplifies the algorithm.
2. Think about scalability: This solution is efficient since the Roman numeral system has fixed rules and symbols.
3. Explain constraints: Confirm the input range (1 to 3999) to clarify assumptions.

📚 Learn More

Check out the full explanation and code walkthrough on my Dev.to post:
👉 Roman to Integer - JavaScript Solution

How would you optimize this further? Let’s discuss below! 🚀

JavaScript #LeetCode #CodingInterview #ProblemSolving