随机生成包含大小写和数字的字符串

写了一个随机产生字符串的方法，字符串由大小字母和数字组成，

我这里利用的是GUID 作为源点，避免重复出现

  /// <summary>
        ///  
        /// </summary>
        /// <param name="leng">长度</param>
        public static void GenerateCheckCode(int leng)
        {
            var num2 = Guid.NewGuid().ToString();
            while(num2.Length<leng-1){num2 += Guid.NewGuid().ToString();}

            int max = new Random().Next(100000, 999999);
            char[] list = new char[leng];
            int[] array = new int[leng] ;

            for (int i = 0; i < leng; i++){array[i] = i;}

            int[] temp;
            temp = new int[array.Length];
            for (int i = 0; i < temp.Length; i++) { temp[i] = array[i]; }
            Random rand = new Random(DateTime.Now.Millisecond);
            for (int i = 0; i < temp.Length; i++)
            {
                int x, y; int t;
                x = rand.Next(0, temp.Length);
                do{y = rand.Next(0, temp.Length);} while (y == x);
                t = temp[x];
                temp[x] = temp[y];
                temp[y] = t;
            }
            for (int i = 0; i < leng; i++)
            {
                if (i %3== 0)
                {
                    list[temp[i]] = (char)(0x30 + ((ushort)(num2[i] * max % 10)));
                }else if (i % 3 == 1)
                {
                    list[temp[i]] = (char)(0x41 + ((ushort)(num2[i] * max % 0x1a)));
                }else if (i % 3 == 2)
                {
                    list[temp[i]] = (char)(0x61 + ((ushort)(num2[i] * max % 0x1a)));
                }
            }
            
            Console.WriteLine(string.Join("", list));
        }