Swift算法实现字符串转数字的方法示例

//字符串转数字
func StrToInt(str:String) -> Int{
 
 //字符串不能为空
 guard str.isEmpty == false else {
 print("字符串不能为空~");
 return 0;
 }
 
 var s = 1
 var strInt:Int? = nil
 
 for characterInt in str.unicodeScalars {
 
 //只能包含数字或正负号
 let tempStrInt = characterInt.hashValue - "0".unicodeScalars.first!.hashValue
 guard (tempStrInt <= 9 && tempStrInt >= 0) || (characterInt.hashValue == 43 || characterInt.hashValue == 45) else {
  
  print("包含非法字符！");
  return 0;
  
 }
 
 //正负号只能存在于字符串开头
 if characterInt.hashValue == 43 || characterInt.hashValue == 45 {
  guard strInt == nil else {
  print("正负号只能存在于字符串开头！");
  return 0;
  }
 }
 
 //既然走到这一步，说明字符串合法
 //判断正负数
 if characterInt.hashValue == 43 || characterInt.hashValue == 45{
  s = s * ( 44 - characterInt.hashValue )
 }else{
  
  if strInt == nil {
  strInt = characterInt.hashValue - "0".unicodeScalars.first!.hashValue
  }else{
  //使用溢出运算符&*和&+避免数值过大导致溢出崩溃
  strInt = strInt! &* 10 &+ ( characterInt.hashValue - "0".unicodeScalars.first!.hashValue ) 
  }
 
 }
 
 }
 
 var result:Int? = 0
 if strInt != nil {
 result = s * strInt!
 }
 
 return result!;
}