Determine if a number is a 'happy number'. A happy number eventually reaches 1 when replaced by the sum of the squares of its digits, repeating the process until it does.

You're given a list of jobs with start times, end times, and profits. Find the maximum profit you can obtain by scheduling a subset of jobs that don't overlap.

You are given k sorted lists. Combine all of their elements into a single sorted list and return it.