//349 public static int[] Intersection(int[] nums1, int[] nums2) { BinarySearchTreeSet <int> binarySearchTreeSet = new BinarySearchTreeSet <int>(); foreach (var num in nums1) { binarySearchTreeSet.Add(num); } List <int> list = new List <int>(); foreach (var num in nums2) { if (binarySearchTreeSet.Contains(num)) { list.Add(num); binarySearchTreeSet.Remove(num); } } return(list.ToArray()); }