day 8 part 2

day08/part2.lua

@@ -0,0 +1,110 @@
+#!/usr/bin/env luajit
+require("utils")
+require("set")
+
+local entries = {}
+for line in io.lines(arg[3]) do
+	local entry = split(line, " ")
+	table.remove(entry, 11)
+	table.insert(entries, entry)
+end
+
+function uniques(segment)
+	if #segment == 2 then return "cf" end
+	if #segment == 3 then return "acf" end
+	if #segment == 4 then return "bcdf" end
+end
+
+function reduceoptions(options, segment)
+	local included = uniques(segment)
+	if included then
+		for part in chars("abcdgef") do
+			if string.find(segment, part) then
+				options[part]:keeponly(chars(included))
+			else
+				options[part]:removeall(chars(included))
+			end
+		end
+	end
+end
+
+function printoptions(options)
+	for from, s in pairs(options) do
+		io.write(from..":")
+		for to in s:iter() do
+			io.write(to)
+		end
+		io.write(" ")
+	end
+	io.write("\n")
+end
+
+function asdigit(segment, sel)
+	local lit = set()
+	for c in chars(segment) do
+		lit:add(sel[c])
+	end
+
+	if lit:equal(set(chars("acbefg"))) then return 0 end
+	if lit:equal(set(chars("cf"))) then return 1 end
+	if lit:equal(set(chars("acdeg"))) then return 2 end
+	if lit:equal(set(chars("acdfg"))) then return 3 end
+	if lit:equal(set(chars("bcdf"))) then return 4 end
+	if lit:equal(set(chars("abdfg"))) then return 5 end
+	if lit:equal(set(chars("abdefg"))) then return 6 end
+	if lit:equal(set(chars("acf"))) then return 7 end
+	if lit:equal(set(chars("abcdefg"))) then return 8 end
+	if lit:equal(set(chars("abcdfg"))) then return 9 end
+end
+
+function backtrack(options, displays, display, segment, acc, sel, rev)
+	if display > #displays then
+		return set({acc})
+	elseif segment <= #displays[display] then
+		local pickfor = char(displays[display], segment)
+		local picked = sel[pickfor]
+		if picked then
+			return backtrack(options, displays, display, segment+1, acc, sel, rev)
+		else
+			local accs = set()
+			for picked in options[char(displays[display], segment)]:iter() do
+				sel[pickfor] = picked
+				if not rev:has(picked) then
+					rev:add(picked)
+					accs:addall(backtrack(options, displays, display, segment+1, acc, sel, rev):iter())
+					rev:remove(picked)
+				end
+			end
+			sel[pickfor] = nil
+			return accs
+		end
+	else
+		local digit = asdigit(displays[display], sel)
+		if digit then
+			return backtrack(options, displays, display + 1, 1, (acc * 10 + digit) % 10000, sel, rev)
+		else
+			return set()
+		end
+	end
+end
+
+function outputvalue(entry)
+	local options = { a = set(chars('abcdefg')),
+	                  b = set(chars('abcdefg')),
+	                  c = set(chars('abcdefg')),
+	                  d = set(chars('abcdefg')),
+	                  e = set(chars('abcdefg')),
+	                  f = set(chars('abcdefg')),
+	                  g = set(chars('abcdefg')) }
+
+	for k, v in pairs(entry) do reduceoptions(options, v) end
+	local solutions = backtrack(options, entry, 1, 1, 0, {}, set())
+	if solutions.size == 1 then
+		return solutions:iter()()
+	else
+		error("meh")
+	end
+end
+
+foreach(entries, outputvalue)
+print(sum(entries))