Pair with sum problem

pairs.rb

# Find a pair of elements from an array whose sum equals a given number
#
# * The array contains only integers
# * The array can have duplicates
# * Return a boolean that indicates if the list has such a pair
# * We will start with an ordered (ascending order) list example

require 'benchmark/ips'
require 'set'

def naive_approach(numbers, sum)
  numbers.combination(2).any? { |a, b| a + b == sum }
end

def has_pairs_with_sum_functional(numbers, sum)
  return false if numbers.size <= 1
  return true if numbers[1..-1].include?(sum - numbers[0])
  has_pairs_with_sum_functional(numbers[1..-1], sum)
end

def has_pair_with_sum_brute_force(input, sum)
  0.upto(input.length - 1) do |n|
    0.upto(input.length - 1) do |i|
      if input[i] + input[n] == sum and n != i
        return true
      end
    end
  end
  return false
end

def has_pair_with_sum_in_unordered_list(input, sum)
  complements = Set.new
  0.upto(input.length - 1) do |i|
    value = input[i]
    complement = sum - value
    # if we have stored the value complement then we have a winner pair
    if complements.include?(value)
      return true
    else
      complements.add(complement)
    end
  end
  return false
end

def test(array, sum = 100)
  Benchmark.ips do |x|
    x.report('Brute Force:') { has_pair_with_sum_brute_force array, sum }
    x.report('Combination:') { naive_approach array, sum }
    x.report('Functional: ') { has_pairs_with_sum_functional array, sum }
    x.report('Set:        ') { has_pair_with_sum_in_unordered_list array, sum }
    x.compare!
  end
end

array = 1.upto(100_000_000).map { rand(100) }
test(array)

Calculating -------------------------------------
        Brute Force:    19.948k i/100ms
        Combination:     3.576k i/100ms
        Functional:     65.712k i/100ms
        Set:            12.560k i/100ms
-------------------------------------------------
        Brute Force:    321.027k (±13.1%) i/s -      1.576M
        Combination:    195.988k (±15.8%) i/s -    954.792k
        Functional:       1.764M (±10.6%) i/s -      8.740M
        Set:            149.611k (±12.9%) i/s -    741.040k

Comparison:
        Functional: :  1763867.2 i/s
        Brute Force::   321027.5 i/s - 5.49x slower
        Combination::   195987.8 i/s - 9.00x slower
        Set:        :   149610.6 i/s - 11.79x slower