lowest_number_concat.rb

# frozen_string_literal: true
#
# Copyright (c) 2016 Pete Hanson

require 'minitest/autorun'

def lowest_number(number_list)
  number_list.map(&:to_s).sort do |a, b|
    if a.start_with?(b)
      a[b.size..-1] <=> b
    elsif b.start_with?(a)
      a <=> b[a.size..-1]
    else
      a <=> b
    end
  end.join('').to_i
end

class TestLowestNumber < Minitest::Test
  def test_1
    assert_equal 1_23_550_80,       lowest_number([23, 550, 1, 80])
  end

  def test_2
    assert_equal 1_1_1_1,           lowest_number([1, 1, 1, 1])
  end

  def test_3
    assert_equal 10000_11_123_1890, lowest_number([10000, 123, 1890, 11])
  end

  def test_4
    assert_equal 1890_11890,        lowest_number([1890, 18901])
  end

  def test_5
    assert_equal 11_12_33_9,        lowest_number([12, 33, 11, 9])
  end

  def test_6
    assert_equal 18_1834_55023_550, lowest_number([55023, 550, 1834, 18])
  end

  def test_7
    assert_equal 1817_18_55023_550, lowest_number([55023, 550, 1817, 18])
  end

  def test_8
    assert_equal 1818_18_55023_550, lowest_number([55023, 550, 1818, 18])
  end

  def test_9
    assert_equal 1_1_1,             lowest_number([1, 1, 0, 1])
  end
end