Find unique common element from 3 arrays

Question

Original Problem:
I have 3 boxes each containing 200 coins, given that there is only one person who has made calls from all of the three boxes and thus the

Answer 1

Let N = 200, k = 3,

1. Create a hash table H with capacity ≥ Nk.

2. For each element X in array 1, set H[X] to 1.

3. For each element Y in array 2, if Y is in H and H[Y] == 1, set H[Y] = 2.

4. For each element Z in array 3, if Z is in H and H[Z] == 2, return Z.

5. throw new InvalidDataGivenByInterviewerException();

O(Nk) time, O(Nk) space complexity.