Roman to Integer

Loading...LeetCode

Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.

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

For example, 2 is written as II in Roman numeral, just two ones added together. 12 is written as XII, which is simply X + II. The number 27 is written as XXVII, which is XX + V + II.

Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is not IIII. Instead, the number four is written as IV. Because the one is before the five we subtract it making four. The same principle applies to the number nine, which is written as IX. There are six instances where subtraction is used:

• I can be placed before V (5) and X (10) to make 4 and 9.

• X can be placed before L (50) and C (100) to make 40 and 90.

• C can be placed before D (500) and M (1000) to make 400 and 900.

Given a roman numeral, convert it to an integer.

Example 1:

Input: s = "III"
Output: 3
Explanation: III = 3.

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 and IV = 4.

Constraints:

• 1 <= s.length <= 15

• s contains only the characters ('I', 'V', 'X', 'L', 'C', 'D', 'M').

• It is guaranteed that s is a valid roman numeral in the range [1, 3999].

You can solve this problem by iterating through the given Roman numeral string and summing up the corresponding values. However, you need to consider the cases where subtraction is used. Here's a JavaScript implementation:

function romanToInt(s) {
    const romanToIntMap = new Map([
        ['I', 1],
        ['V', 5],
        ['X', 10],
        ['L', 50],
        ['C', 100],
        ['D', 500],
        ['M', 1000]
    ]);

    let result = 0;

    for (let i = 0; i < s.length; i++) {
        const currentSymbol = s[i];
        const nextSymbol = s[i + 1];

        if (nextSymbol && romanToIntMap.get(currentSymbol) < romanToIntMap.get(nextSymbol)) {
            result -= romanToIntMap.get(currentSymbol);
        } else {
            result += romanToIntMap.get(currentSymbol);
        }
    }

    return result;
}

// Test cases
console.log(romanToInt("III"));     // Output: 3
console.log(romanToInt("LVIII"));   // Output: 58
console.log(romanToInt("MCMXCIV")); // Output: 1994

This romanToInt function iterates through the given Roman numeral string s. For each symbol, it checks if the next symbol has a greater value. If so, it subtracts the current value from the result; otherwise, it adds it. Finally, it returns the accumulated result.