June Code Challenge: 5 HackerRank Problems

Details
This month, we'll discuss five problems selected from HackerRank. Two are described as "easy" difficulty, two as "medium", and one as "hard". Among other things, they should be useful as preparation for tech interviews and for learning about algorithms.
This will be a casual meeting. You don't need to have worked on all - or any! - of the problems before coming. Those of us who have finished solutions can discuss the approaches we took and what we learned along the way, and those who are still working are welcome to talk through any difficulties you're encountering.
Last time, several people commented that a projector would have been helpful. So we'll be in the "Large Meeting Room" this time, which has one.
Here are the problems:
- Sock Merchant: https://www.hackerrank.com/challenges/sock-merchant
- Ransom Note: https://www.hackerrank.com/challenges/ctci-ransom-note
- Count Triplets: https://www.hackerrank.com/challenges/count-triplets-1
- Special Palindrome Again: https://www.hackerrank.com/challenges/special-palindrome-again
- Maximum Subarray Sum: https://www.hackerrank.com/challenges/maximum-subarray-sum

June Code Challenge: 5 HackerRank Problems