prefix_set.rb

# full description: 
# https://codility.com/demo/take-sample-test/ps/

# tl;dr: Write a function that, given a zero-indexed non-empty array A consisting of N integers, returns the first covering prefix of A.

def solution(a)
  last_unique = a.uniq.last
  a.index { |el| el == last_unique }
end

array = (0..1_000_000).to_a
puts Benchmark.measure {
  expect(solution(array)).to eq(1_000_000)
} # => 0.36s