随机洗牌

        private static void sum(int[] nums)
        {
            Random rnd = new Random();
            for(int i=nums.Length-1; i>=0; i--)
            {
                int a= rnd.Next(i + 1);
                //Console.WriteLine(a);
                int tmpe=nums[a];
                nums[a] = nums[i];
                nums[i]= tmpe;
                //Console.WriteLine(nums.Length);


            }
            for (int j = 0; j < nums.Length; j++)
            {
                Console.WriteLine(nums[j]);
            }
        }