test.rb

def foobar n=100
  (1..n).each do |i|
    output = "#{'Hi' if i % 3 == 0}#{'By' if i % 5 == 0}"
    output = i.to_s if output.empty?
    puts output
  end
end

def swapcase str
  str.chars.map{ |c| c == c.downcase ? c.upcase : c.downcase }.join
  # Or just str.swapcase
end

# Let me know if you use DP on a daily basis!
# https://leetcode.com/problems/word-break/solutions/3454380/python3-dp-bottom-up-with-step-by-step-explanation/
# https://leetcode.com/problems/triangle/solutions/3646355/from-brute-force-to-dp-with-o-n-space-in-ruby/

# This one I've actually coded myself some time ago:
def max_subarray nums
  return 0 if nums.empty?
  dp = nums.map(&:clone)
  result = dp[0]

  (1..nums.size - 1).each do |i|
    dp[i] = [nums[i], nums[i] + dp[i - 1]].max
    result = [result, dp[i]].max
  end
  result
end

# Last task relatively looks like a TSP: https://en.wikipedia.org/wiki/Travelling_salesman_problem