Question

I recently found a question that went something like:

"Given an array of strings, return the number of distinct strings in that array."

I came up with this solution:

1. Get number_of_strings, which equals the number of strings in the input array
2. Get number_of_non_redundant, which equals the length of the input array cast as a set
3. Return 2 times number_of_non_redundant - number_of_strings

So, my question is, does this algorithm work for all data sets?

Answer 1

As others have pointed out, simply returning number_of_non_redundant seems like the answer to this problem.

Here is a possible solution for determining number_of_non_redundant:

1) Create a Hash Set (Language specific)

2) Iterate through the entire array, on each element of the array
check to see if the element exists in the Hash Set, if it doesn’t, add
it.

3) Return the size of the Hash Set.

Using a Hash Set here offers constant time operations(add, contains).

Additionally I wanted to point out that you can’t (at least I am not aware of this in a language) simply cast an array to a set. Casting is a constant time operation. These are two different data structures and in order to take elements from an array and place them in a set, it would require iterating through the array and entering the elements into a set.