Tech Qu: Intersect two arrays

Write the code to find the intersection of two arrays, a,b.

 

The code can be very simple (or horribly complex) from the right perspective:

Code Snippet

1. public static int[] IntersectionArray(int[] arr, int[] arr2)
2. {
3.   var result = new HashSet<int>();
4.   var map = new HashSet<int>();
5.   foreach (var i in arr)
6.   //  if (!map.Contains(i))
7.       map.Add(i);
8.   foreach (var i in arr2)
9.     if (map.Contains(i) )// && !result.Contains(i))
10.       result.Add(i);
11.   return result.ToArray();
12. }

 

I have included some unneeded condition tests as comments above (HashSet does not retain duplicates and it is assumed that an explicit test would be more expensive then letting the hashset do it itself).

 

Unit testing is trivial

Code Snippet

1. int[] a = { 1, 2, 3, 4, 5, 6, 5, 6 };
2. int[] b = { 3, 4, 3, 4, 3, 4, 3, 4, };
3. var test = Questions.IntersectionArray(a, b);
4. foreach (var i in test)
5. {
6.   Console.WriteLine(i);
7. }

The results in just {3,4}