Two Out of Three - Solution & Explanation

To solve the problem, we'll use sets to capture unique elements from each array, then count the total appearances of each element across all arrays. Finally, we'll select elements that appear in at least two arrays.

The approach involves converting each array into a set to fetch distinct elements. We then use a dictionary (or map) to track the frequency of each element appearing across the three sets.

The function twoOutOfThree creates sets for each input list to get unique values from them. It uses a dictionary to count how many sets each element appears in. Finally, it returns a list of elements that appear in at least two sets.

This method employs auxiliary arrays to record the presence frequency of elements. Given the constraint that elements are between 1 and 100, we can use a fixed-size frequency array to track how many of the three arrays contain any given element.

This Python solution uses a frequency array of size 101 to count how many times a number is present in the three arrays. By marking the frequency for unique elements in each list, the solution considers elements appearing in at least two arrays.