Programming challenges

I'm tracking here the solutions for problems on some of the programming challenges websites that we have, such as:

• coderbyte - https://www.coderbyte.com/
• codewars - https://www.codewars.com/
• codility - https://www.codility.com/ - https://app.codility.com/programmers/lessons
• HackerRank - https://www.hackerrank.com/
• leetCode - https://leetcode.com/
• ProjectEuler - http://projecteuler.net/
• UVa - https://onlinejudge.org/

I'm trying to keep the link for the problem inside the file but for some it got lost. Please forgive me for some poor variable naming, some of the solutions (the easy ones of course) I've coded on my phone while I was on a line waiting for something or passing the time.