RomanToInteger.swift

/**
 * Question Link: https://leetcode.com/problems/roman-to-integer/
 * Primary idea: Iterate through end to start, add or minus according to different situations
 * Time Complexity: O(n), Space Complexity: O(n)
 *
 */

class RomanToInteger {
    func romanToInt(s: String) -> Int {
        let dict = initDict()
        let chars = [Character](s.characters.reverse())
        var res = 0
        
        for i in 0..<chars.count {
            guard let current = dict[String(chars[i])] else {
                return res
            }
            if i > 0 && current < dict[String(chars[i - 1])] {
                res -= current
            } else {
                res += current
            }
        }
        
        return res
    }
    
    private func initDict() -> [String: Int] {
        var dict = [String: Int]()
        
        dict["I"] = 1
        dict["V"] = 5
        dict["X"] = 10
        dict["L"] = 50
        dict["C"] = 100
        dict["D"] = 500
        dict["M"] = 1000
        
        return dict
    }
}