Inefficient Membership Test (ARCH6075)

Key ruby.performance.inefficient-membership-test · Severity warning · Category performance

Checking membership with include? on an array is O(n); repeated in a loop it becomes O(n*m). Use a Set to make the lookup O(1).

Incorrect

def allowed(ids, blocked)
  ids.select { |id| !blocked.include?(id) }
end

Correct

require "set"

def allowed(ids, blocked)
  blocked_set = blocked.to_set
  ids.select { |id| !blocked_set.include?(id) }
end

Fix

Convert the array to a Set for repeated membership checks and benefit from O(1) lookups.