test.rb

class Test
  # [2, 1, 3, 5, 3, 2]
  def performance(array) O(n) 
    hash = {}

    array.each do |element| # 2
      if hash[element] # {} , { 2 => true }, { 2 => true, 1 => true }, { 2 => true, 1 => true, 3 => true} ...
        return element # => si existe retorna 3
      else
        hash[element] = true
      end
    end
    -1
  end

  def main # O(n2)
    array = [2, 1, 3, 5, 3, 2]
    dupli = []

    array.each_with_index do |element, index|
      if array.index(element) != index && !dupli.include?(element)
        dupli << element
      end
    end

    if dupli.empty?
      return -1
    end

    return dupli[0]
  end
end

RSpec.describe '#performance' do
  it 'input [2, 1, 3, 5, 3, 2]' do
    expect(Test.new.performance([2, 1, 3, 5, 3, 2])).to eq(3)
  end

  it 'input [2, 4, 3, 5, 1]' do
    expect(Test.new.performance([2, 4, 3, 5, 1])).to eq(-1)
  end

  it 'input [1]' do
    expect(Test.new.performance([1])).to eq(-1)
  end

  it 'input [2, 2]' do
    expect(Test.new.performance([2, 2])).to eq(2)
  end

  it 'input [2, 1]' do
    expect(Test.new.performance([2, 1])).to eq(-1)
  end

  it 'input [2, 1, 3]' do
    expect(Test.new.performance([2, 1, 3])).to eq(-1)
  end

  it 'input [2, 3, 3]' do
    expect(Test.new.performance([2, 3, 3])).to eq(3)
  end

  it 'input [3, 3, 3]' do
    expect(Test.new.performance([3, 3, 3])).to eq(3)
  end

  it 'input [8, 4, 6, 2, 6, 4, 7, 9, 5, 8]' do
    expect(Test.new.performance([8, 4, 6, 2, 6, 4, 7, 9, 5, 8])).to eq(6)
  end

  it 'input [10, 6, 8, 4, 9, 1, 7, 2, 5, 3]' do
    expect(Test.new.performance([10, 6, 8, 4, 9, 1, 7, 2, 5, 3])).to eq(-1)
  end

  it 'input [1, 1, 2, 2, 1]' do
    expect(Test.new.performance([1, 1, 2, 2, 1])).to eq(1)
  end
end