My answer to "Five programming problems every Software Engineer should be able to solve in less than 1 hour"

README.md

My answer to Santiago's post : "Five programming problems every Software Engineer should be able to solve in less than 1 hour"

Note:

• I spent about an hour and a half on five problems.
• I have no idea how to solve problem 4 and problem 5 with low complexity. So I have solved problem 4 and problem 5 using *brute-force" algorithm.

problem1.rb

require 'minitest/autorun'


def sum_for_loop(list)
  sum = 0
  for item in list
    sum = sum + item
  end
  sum
end

def sum_while_loop(list)
  sum = 0
  i = 0
  while (i < list.length)
    sum = sum + list[i]
    i = i + 1
  end
  sum
end

def sum_recursion(list)
  if list.length == 1
    list[0]
  else
    list[0] + sum_recursion(list.slice(1, list.length - 1))
  end
end


class TC_Problem1 < MiniTest::Test
  def test_sum_for_loop()
    assert_equal([1, 3, 5, 9].inject(:+), sum_for_loop([1, 3, 5, 9]))
  end
  def test_sum_while_loop()
    assert_equal([1, 3, 5, 9].inject(:+), sum_while_loop([1, 3, 5, 9]))
  end
  def test_sum_recursion()
    assert_equal([1, 3, 5, 9].inject(:+), sum_recursion([1, 3, 5, 9]))
  end
end

problem2.rb

require 'minitest/autorun'

def combine_alternatingly(list1, list2)
  a = list1.dup
  b = list2.dup
  out = []
  while (a.length > 0) || (b.length > 0)
    out << a.shift if a.length > 0
    out << b.shift if b.length > 0
  end
  out
end


class TC_Problem2 < MiniTest::Test
  def test_combine_alternatingly()
    assert_equal([:a, 1, :b, 2, :c, 3], combine_alternatingly([:a, :b, :c], [1, 2, 3]))
  end
end

problem3.rb

require 'minitest/autorun'

def fibo(length=100)
  array = [0, 1]
  i = 2
  while i < length
    array[i] = array[i - 1] + array[i - 2]
    i = i + 1
  end
  array
end


class TC_Problem3 < MiniTest::Test
  def test_fibo()
    assert_equal([0, 1, 1, 2, 3, 5, 8, 13, 21, 34], fibo(10))
    
    fibo100 = fibo()
    assert_equal(100, fibo100.length)
    assert_equal(fibo100[98] + fibo100[97], fibo100[99])
  end
end

problem4.rb

require 'minitest/autorun'

def arrange_largest_num(list)
  nums = list.dup
  max_nums_array = [nums.shift]
  while nums.length > 0
    n = nums.shift
    max_nums_array = (0..(max_nums_array.length)).map { |i|
      [max_nums_array.slice(0, i), n, max_nums_array.slice(i, max_nums_array.length - i)].flatten
    }.max { |a,b|
      a.join('').to_i <=> b.join('').to_i
    }
  end

  max_nums_array.join('').to_i
end

class TC_Problem4 < MiniTest::Test
  def test_arrange_largest_num()
    assert_equal(95021, arrange_largest_num([50, 2, 1, 9]))

    # pointed by Kevin Tran
    assert_equal(42423420, arrange_largest_num([420, 42, 423]))
  end
end

problem5.rb

def all_poss_100()
  (0..(3**8-1)).map { |v|
    s = v.to_s(3)
    s = '0' * (8 - s.length) + s
  }.map { |v|
    s = ''
    (0..(8-1)).each do |i|
      s << (i + 1).to_s
      s << '+' if v[i] == '0'
      s << '-' if v[i] == '1'
      s << ''  if v[i] == '2'
    end
    s << '9'
    s
  }.select { |v|
    eval(v) == 100
  }
end

def print_all_poss_100()
  $stdout << all_poss_100.join("\n") << "\n"
end

print_all_poss_100