Roman to Integer Conversion

Given a string s representing a Roman numeral, find it's corresponding integer value.
Roman numerals are formed using the following symbols: I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, and M = 1000.
Numbers are typically formed by combining these symbols from left to right, adding or subtracting their values based on specific rules.

How does the conversion work?

• If a smaller value symbol comes before, we subtract. Otherwise, we add.
• In IV, I comes before V and V has a larger value 5. So our result is 5 - 1 = 4.
• In VI, V comes before I and I has a smaller value 1. So our result is 5 + 1 = 6.
• In II, we have same values, so we add and get 1 + 1 = 2
• In case of more than 2 characters, we traverse from left to right and group only when we see a greater value character after a smaller value character. For example MXVII is 1000 + 10 + 5 + 1 + 1 = 1017. And XLVII is (50 - 10) + 5 + 1 + 1 = 47. Note that L is larger and comes after X.

Examples:

Input: s = "IX"
Output: 9
Explanation: IX is a Roman symbol which represents 10 - 1 = 9

Input: s = "XL"
Output: 40
Explanation: XL is a Roman symbol which represents 50 - 10 = 40

Input: s = "MCMIV"
Output: 1904
Explanation: M is 1000, CM is 1000 - 100 = 900, and IV is 4. So we have total as 1000 + 900 + 4 = 1904

[Expected Approach 1] Using Iterative Comparison - O(n) time and O(1) space

The idea for converting a Roman numeral to an integer is that, we have to traverse the string from left to right. For each symbol compare it with the next symbol (if it exists). If the current symbol is greater than or equal to the next symbol then add its value to the result. Otherwise, subtract its value from the next symbol's value and add the result to the total, and skip the next symbol.

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[Expected Approach 2] Using Hashing - O(n) time and O(1) space

We can use an hash map or dictionary to store the values of Roman symbols. And to solve the problem, we have to iterate through the string and for each symbol, check if the current value is less than the next value. If so, subtract the current value from the next value and add the result to the total. Otherwise, add the current value to the total.

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