C#通过yield实现数组全排列的方法

static void Swap<T>(ref T a, ref T b)
{
 T t = a;
 a = b;
 b = t;
}
static IEnumerable<int[]> Perm(int[] arr, int pos)
{
 if (pos == arr.Length)
 {
  yield return arr;
 }
 for (int i = pos; i < arr.Length; ++i)
 {
  Swap(ref arr[i], ref arr[pos]);
  foreach (var j in Perm(arr, pos + 1)) yield return j;
  Swap(ref arr[i], ref arr[pos]);
 }
}
static void Main(string[] args)
{
 foreach (var i in Perm(new int[] { 1, 2, 3, 4 }, 0))
 {
  Console.WriteLine(string.Join(",",i.Select(j=>j.ToString()).ToArray()));
 }
}