Print a square matrix in snake pattern

snake_matrix.rb

puts "n:"
n = gets.to_i
matrix = Array.new(n){Array.new(n, 0)}

def snake(n, matrix, i, j, num)
  if num == n * n
    matrix[i][j] = num
    return num
  end
  matrix[i][j] = num
  if (i == 0 || i == n - 1) && j % 2 != 0
    if j < n - 1
      return snake(n, matrix, i, j + 1, num + 1)
    else
      return snake(n, matrix, i + 1, j, num + 1)
    end
  end

  if (j == 0 || j == n - 1) && i % 2 == 0
    return snake(n, matrix, i + 1, j, num + 1)
  end

  if (i + j) % 2 == 0
    return snake(n, matrix, i + 1, j - 1, num + 1)
  else
    return snake(n, matrix, i - 1, j + 1, num + 1)
  end
end

snake(n, matrix, 0, 0, 1)

for i in 0...n
  for j in 0...n
    print "#{ matrix[i][j]} #{matrix[i][j].to_s.split('').length > 1 ? " ": " "}"
  end
  print "\n"
end