second.exs

# The spreadsheet consists of rows of apparently-random numbers. 
# To make sure the recovery process is on the right track, they need you to calculate the spreadsheet's checksum. 
# For each row, determine the difference between the largest value and the smallest value; the checksum is the sum of all of these differences.
# For example, given the following spreadsheet:
# 5 1 9 5
# 7 5 3
# 2 4 6 8
# The first row's largest and smallest values are 9 and 1, and their difference is 8.
# The second row's largest and smallest values are 7 and 3, and their difference is 4.
# The third row's difference is 6.
# In this example, the spreadsheet's checksum would be 8 + 4 + 6 = 18.

s1="""
PUT YOUR SPREADSHEET HERE
"""

defmodule Second do
	def checksum_for_spreadsheet(spreadsheet) do
		# spreadsheet is a list of lists
		# it's pass
		prep_spreadsheet(spreadsheet) |> checksum
	end

	defp prep_spreadsheet(spreadsheet_string) do
		# ok split this into rows by newline
		String.split(spreadsheet_string, "\n")
	end

	defp checksum([]) do
		# empty list, so return 0
		0
	end

	defp checksum(rows) do
		# the first call on a list with at least one thing
		IO.puts("There are " <> Integer.to_string(length(rows)) <> " rows")
		checksum(rows, 0)
	end

	defp checksum([], sum) do
		# the last call - the list is now empty, so return the sum. this is the sum of all lists
		sum
	end

	defp checksum([head | tail], sum) do
		# where we do all the hard work
		# first let's get a list of integers
		row_str = String.split(head)
		row_int = Enum.map(row_str, fn(x) -> String.to_integer(x) end)
		# now, you get the highest and lowest values in the head, which is the row
		# then you get the difference
		# ok maybe we'll do that together
		diff = row_difference(row_int)
		IO.puts("Now the sum is " <> Integer.to_string(sum + diff))
		checksum(tail, sum+diff) # less ugly by far
	end

	defp row_difference([]) do
		0
	end

	defp row_difference(list) do
		# the way in
		row_difference(list, 0)
	end

	defp row_difference([head | tail], high) when head > high do
		row_difference(tail, head)
	end

	defp row_difference([head | tail], high) when head < high do
		row_difference(tail, high, head)
	end

	defp row_difference([head | tail], high, low) when head > high do
		# replace the top value
		row_difference(tail, head, low)
	end

	defp row_difference([head | tail], high, low) when head < low do
		# replace lowest value
		row_difference(tail, high, head)
	end

	defp row_difference([head | tail], high, low) do
		row_difference(tail, high, low)
	end

	defp row_difference([], high, low) do
		IO.puts("The high is " <> Integer.to_string(high) <> " and the low is " <> Integer.to_string(low) <> " with a diff of " <> Integer.to_string(high-low))
		high - low
	end
 end

IO.puts(Second.checksum_for_spreadsheet(s1))