snail.rb

def snail(array)
  x = 0
  y = 0
  done = []
  indexes = [[1,0],[0,1],[-1,0],[0,-1]].cycle
  delta = indexes.next
  res = []
  array.flatten.length.times do |n|
    res << array[y][x]
    done << x.to_s+y.to_s
      x = x+delta[0]
      y = y+delta[1]
    if (done.include?(x.to_s+y.to_s) ||
        array[y].nil? || array[y][x].nil? ||
        y < 0 || x < 0)
      x = x-delta[0]
      y = y-delta[1]
      delta = indexes.next
      x = x+delta[0]
      y = y+delta[1]
    end
  end
  res
end



def snail(array)
  array.empty? ? [] : array.shift + snail(array.transpose.reverse)
end



#Test
def test input , expected
  array = [[ 1, 2, 3, 4, 5],
           [ 6, 7, 8, 9,10],
           [11,12,13,14,15],
           [16,17,18,19,20],
           [21,22,23,24,25]]
  expected = [1,2,3,4,5,10,15,20,25,24,23,22,21,16,11,6,7,8,9,14,19,18,17,12,13]
  resut = snail(array)
  expected == result
end