Roman numerals to Int method

Solution.swift

import Foundation

class Solution {
    
    func romanToInt(_ s: String) -> Int {
        var stringVar = s
        print("stringVar: \(stringVar)")
        var num = 0
        
        let validDic = [
            "I": 1,
            "V": 5,
            "X": 10,
            "L": 50,
            "C": 100,
            "D": 500,
            "M": 1000,
        ]
        
        let exceptionsDic = [
            "IV": 4,
            "IX": 9,
            "XL": 40,
            "XC": 90,
            "CD": 400,
            "CM": 900
        ]
        
        var counter = 0
        
        for char in stringVar {
            let isValid = validDic.contains(where: { (string, integer) in
                string.contains(char)
            })
            if isValid == false {
                print("String does not contain a valid Roman numeral.")
                return -1
            }
            if counter < stringVar.count - 1 {
                let isException = exceptionsDic.contains { (string, integer) in
                    let i = stringVar.index(stringVar.startIndex, offsetBy: counter, limitedBy: stringVar.endIndex)
                    let j = stringVar.index(stringVar.startIndex, offsetBy: counter + 1, limitedBy: stringVar.endIndex)
                    var k = stringVar[i!]
                    let l = stringVar[j!]
                    var m: String = ""
                    m.append(k)
                    m.append(l)
                    
                    if string.contains(m) == true {
                        print("true_m: \(m), stringVar: \(stringVar)")
                        num += exceptionsDic[m]!
                        //Remove the first two Characters
                        stringVar.remove(at: i!)
                        stringVar.remove(at: i!)
                        print("stringVar: \(stringVar)")
                        counter = 0
                        return true
                    } else {
                        print("false_m: \(m), stringVar: \(stringVar)")
                        var charS: String = ""
                        charS.append(char)
                        num += validDic[charS]!
                        //Remove only the first Character
                        stringVar.remove(at: i!)
                        print("stringVar: \(stringVar)")
                        counter = 0
                        return false
                    }
                }
            }
            counter += 1
        }
        return num
    }
}