Module:User:Cscott/Advent Of Code/2024/Day 5

return (function()
local builders = {}
local function register(name, f)
  builders[name] = f
end
register('advent.compat', function() return require [[Module:User:Cscott/compat]] end)

register('llpeg.lpegrex', function() return require [[Module:User:Cscott/lpegrex]] end)

register('util', function(myrequire)
local function read_wiki_input(func)
    return function (frame, ...)
      if type(frame)=='string' then
        frame = { args = { frame, ... } }
      end
      local title = mw.title.new(frame.args[1])
      local source = title:getContent()
      if source == nil then
        error("Can't find title " .. tostring(title))
      end
      source = source:gsub("^%s*<syntaxhighlight[^>]*>\n?", "", 1)
      source = source:gsub("</syntaxhighlight[^>]*>%s*$", "", 1)
      return func(source, frame.args[2], frame.args[3])
    end
end

return {
  read_wiki_input = read_wiki_input,
}

end)

register('day5', function(myrequire)
--[[
   Day 5, first part; advent of code 2024
]]--

local compat = myrequire('advent.compat')
local lpegrex = myrequire('llpeg.lpegrex')
local read_wiki_input = myrequire('util').read_wiki_input

--[[ PARSING ]]--
local patt = lpegrex.compile([[
Puzzle <== nl* {:rule: Rules :} nl+ {:pagelist: PageLists :} nl*
Rules <== (Rule nl)+
Rule <== {:before: Number :} `|` {:after: Number :}
PageLists <== PageList (nl PageList)*
PageList <== Number (`,` Number)*
Number <-- %d+ -> tonumber
nl <- %nl
SKIP <- [ ]*
NAME_SUFFIX <- [_%w]+
]])

local Puzzle = {}
Puzzle.__index = Puzzle

function parse(source)
   --print(inspect(source))
   local ast, errlabel, pos = patt:match(source)
   if not ast then
      local lineno, colno, line = lpegrex.calcline(source, pos)
      local colhelp = string.rep(' ', colno-1)..'^'
      error('syntax error: '..lineno..':'..colno..': '..errlabel..
            '\n'..line..'\n'..colhelp)
   end
   --print('Parsed with success!')
   --print(inspect(ast))
   -- turn this into a datastructure
   setmetatable(ast, Puzzle)
   ast:computeIndex()
   return ast
end

--[[
   Infrastructure
]]--

function part1(s)
   return day5a(parse(s))
end

function part2(s)
   return day5b(parse(s))
end

--[[
   Part 1
]]--

function Puzzle:computeIndex()
   self.before = {}
   for i=1,#self.rule do
      local r = self.rule[i]
      if self.before[r.before] == nil then
	 self.before[r.before] = {}
      end
      table.insert(self.before[r.before], r.after)
   end
   for i=1,#self.pagelist do
      local l = self.pagelist[i]
      l.ordinal = {}
      for j=1,#l do
	 l.ordinal[l[j]] = j
      end
   end
end

function Puzzle:checkList(i)
   local list = self.pagelist[i]
   for i=1,#list do
      -- is there a before constraint for this?
      local val = list[i]
      for _,after in ipairs(self.before[val] or {}) do
	 local b = list.ordinal[val]
	 local a = list.ordinal[after]
	 if a ~= nil and b >= a then
	    return false
	 end
      end
   end
   return true
end

function middleList(l)
   local mid = 1 + math.floor(#l / 2)
   return l[mid]
end

function day5a(puzzle)
   local sum = 0
   for i=1,#puzzle.pagelist do
      if puzzle:checkList(i) then
	 -- this is in the correct order.  find the middle page number
	 sum = sum + middleList(puzzle.pagelist[i])
      end
   end
   return sum
end

--[[
Part 2!
]]--

function Puzzle:reorder(i)
   -- clean up list
   local l = {}
   for _,v in ipairs(self.pagelist[i]) do
      table.insert(l, v)
   end
   -- sort list
   local f = function(a,b)
      for _,after in ipairs(self.before[a] or {}) do
	 if after == b then
	    return true
	 end
      end
      return false
   end
   table.sort(l, f)
   return l
end

function day5b(puzzle)
   local sum = 0
   for i=1,#puzzle.pagelist do
      if not puzzle:checkList(i) then
	 local newList = puzzle:reorder(i)
	 -- this is in the correct order.  find the middle page number
	 sum = sum + middleList(newList)
      end
   end
   return sum
end


--[[
   Testing
]]--

--[[
io.write("Sum: ", day5a(parse(io.input("day5.example"):read("a"))), "\n")
io.write("Sum: ", day5a(parse(io.input("day5.input"):read("a"))), "\n")

io.write("Sum: ", day5b(parse(io.input("day5.example"):read("a"))), "\n")
io.write("Sum: ", day5b(parse(io.input("day5.input"):read("a"))), "\n")
]]--

return {
   part1 = read_wiki_input(part1),
   part2 = read_wiki_input(part2),
}

end)

local modules = {}
modules['bit32'] = require('bit32')
modules['string'] = require('string')
modules['strict'] = {}
modules['table'] = require('table')
local function myrequire(name)
  if modules[name] == nil then
    modules[name] = true
    modules[name] = (builders[name])(myrequire)
  end
  return modules[name]
end
return myrequire('day5')
end)()