8. String to Integer (atoi)

StringToInteger(atoi).swift

class Solution {
    func myAtoi(_ str: String) -> Int {
        
        guard str.count > 0 else {
            return 0
        }
        
        var trimmedStr = str.trimmingCharacters(in: .whitespaces)
        
        guard trimmedStr.count > 0 else {
            return 0
        }
        
        
        var resStr: String = ""
        
        var isMinus = false
        
        if trimmedStr.first! == "-" {
            isMinus = true
            trimmedStr.removeFirst()
        } else if trimmedStr.first! == "+" {
            trimmedStr.removeFirst()
        }
        
        var arr = Array(trimmedStr)
        
        for i in 0 ..< arr.count {        
            if arr[i].isNumber == false {
                break
            }
            resStr += "\(arr[i])"
        }
        
        if isMinus == true {
            resStr = "-\(resStr)"
        }
        guard let resDouble = Double(resStr) else {
            return 0
        }
        
        if resDouble > Double(Int32.max) {
            return Int(Int32.max)
        }
        
        if resDouble < Double(Int32.min) {
            return Int(Int32.min)
        }
        
        let resInt = Int(resDouble)
        
        return resInt
    }
}