pascal triangle (naive)

pascal_triangle.rb

require 'test/unit'

#Every number in Pascal's triangle is calculated by adding the numbers to the left and right of it from
#the row above it. For example, the first 4 in the 5th row is found by
#adding the 1 and the 3 from above it in the 4th row.
#
#Write a function pascal(n) that calculates the nth row of Pascal's Triangle,
#and return it as an array of integers.

def solution(n)
  return [] if n == 0
  return [1] if n == 1
  return [1, 1] if n == 2
  result = [[1], [1, 1]]

  (2.upto(n-1)).each do |x|
    previous_row = result[x-1]
    current_row = Array.new(x+1)
    current_row[0] = current_row[x] = 1

    previous_row_index = 1
    1.upto(current_row.size-2) do |y|
      current_row[y] = previous_row[previous_row_index] + previous_row[previous_row_index-1]
      previous_row_index += 1
    end

    result << current_row
  end

  result[n-1]
end

class TestPascalTriangle < Test::Unit::TestCase
  def test_solution
    assert_equal([1], solution(1))
    assert_equal([1,1], solution(2))
    assert_equal([1,2,1], solution(3))
    assert_equal([1,3,3,1], solution(4))
    assert_equal([1,4,6,4,1], solution(5))
    assert_equal([1,5,10,10,5,1], solution(6))
    assert_equal([1,6,15,20,15,6,1], solution(7))
  end
end