C#范围内随机取值，不重复且全部取完

        static void Main(string[] args)        {            List<string> arr = new List<string>();            arr.Add("red");            arr.Add("green");            arr.Add("blue");            arr.Add("orange");            arr.Add("white");            List<string> a = new List<string>();            foreach (var ar in arr)            {                bool flag = true;                while (flag)                {                    string s = GetRandom(arr);                    if (a.Contains(s))                    {                    }                    else                    {                        a.Add(s);                        flag = false;                    }                }            }        }        public static string GetRandom(List<string> arr)        {            Random ran = new Random();            int n = ran.Next(arr.Count);            return arr[n];        }