I was asked questions using hackerrank and below questions were asked:

1. Maximum profit that can be achieved if we trade on non consecutive days. E.g. if we are given an array of [10,-20,30,40,5] the answer is 50 as we can trade on day0 and day3. Alongwith the profit , we have to return the days. I couldn't answer the question but found the answer later using dynamc programming. This is similar to the question: https://leetcode.com/problems/house-robber/
2. Minimum number of swaps required to balance a parantheses. E.g. string value is '))(('.
   The mininum number of swaps is 1 as we can swap the 1st and last position to make it balanced, that is, ()(). I couldn't answer this. I could answer in 0(n^2) by having two loops. But, I think this can be solved using single loop. Appreciate any help.
3. Was asked to design ecommerce website and app. Questions were aksed about REST API and the entity relationship etc. Was able to answer this.