Find duplicates in an array

find-duplicates.rb

require 'benchmark'
require 'set'

array_size = (ENV['TOTAL'] || 1_000_000).to_i
max_int = array_size / 5
array = 1.upto(array_size).map { rand(max_int) }

if ENV['CHECK']
  @correct = array.group_by { |e| e }.select { |k, v| v.size > 1 }.keys.sort
end

def check_answer(answer)
  if ENV['CHECK']
    puts '[Checking answer]'
    fail 'Wrong answer' unless answer.to_a.sort == @correct
  end
end

Benchmark.bmbm do |x|
  x.report 'group_by.select.keys (greater than)' do
    check_answer  array.group_by { |e| e }.select { |k, v| v.size > 1 }.keys
  end

  x.report 'group_by.select.keys (not equal)' do
    check_answer array.group_by { |e| e }.select { |k, v| v.size != 1 }.keys
  end

  x.report 'sort.chunk.select (not equal)' do
    check_answer array.sort.chunk { |e| e }.select { |e, count| count.size != 1 }.map(&:first)
  end

  x.report 'sort.chunk.select (greater than)' do
    check_answer array.sort.chunk { |e| e }.select { |e, count| count.size > 1 }.map(&:first)
  end

  x.report 'iterate with set' do
    found = Set.new
    duplicates = Set.new
    array.select do |e|
      if found.member?(e)
        duplicates.add(e)
        false
      else
        found.add(e)
        true
      end
    end
    check_answer duplicates
  end

  if ENV['SLOW']
    x.report 'select.rindex' do
      check_answer array.select { |e| array.rindex(e) != array.index(e) }.uniq
    end

    x.report 'select.count.uniq' do
      check_answer array.select { |e| array.count(e) > 1 }.uniq
    end
  end
end