In the 2020 grid below, four numbers along a diagonal line have been marked in red.

08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 08
49 49 99 40 17 81 18 57 60 87 17 40 98 43 69 48 04 56 62 00
81 49 31 73 55 79 14 29 93 71 40 67 53 88 30 03 49 13 36 65
52 70 95 23 04 60 11 42 69 24 68 56 01 32 56 71 37 02 36 91
22 31 16 71 51 67 63 89 41 92 36 54 22 40 40 28 66 33 13 80
24 47 32 60 99 03 45 02 44 75 33 53 78 36 84 20 35 17 12 50
32 98 81 28 64 23 67 10 26 38 40 67 59 54 70 66 18 38 64 70
67 26 20 68 02 62 12 20 95 63 94 39 63 08 40 91 66 49 94 21
24 55 58 05 66 73 99 26 97 17 78 78 96 83 14 88 34 89 63 72
21 36 23 09 75 00 76 44 20 45 35 14 00 61 33 97 34 31 33 95
78 17 53 28 22 75 31 67 15 94 03 80 04 62 16 14 09 53 56 92
16 39 05 42 96 35 31 47 55 58 88 24 00 17 54 24 36 29 85 57
86 56 00 48 35 71 89 07 05 44 44 37 44 60 21 58 51 54 17 58
19 80 81 68 05 94 47 69 28 73 92 13 86 52 17 77 04 89 55 40
04 52 08 83 97 35 99 16 07 97 57 32 16 26 26 79 33 27 98 66
88 36 68 87 57 62 20 72 03 46 33 67 46 55 12 32 63 93 53 69
04 42 16 73 38 25 39 11 24 94 72 18 08 46 29 32 40 62 76 36
20 69 36 41 72 30 23 88 34 62 99 69 82 67 59 85 74 04 36 16
20 73 35 29 78 31 90 01 74 31 49 71 48 86 81 16 23 57 05 54
01 70 54 71 83 51 54 69 16 92 33 48 61 43 52 01 89 19 67 48

The product of these numbers is 26 63 78 14 = 1788696.

What is the greatest product of four adjacent numbers in any direction (up, down, left, right, or diagonally) in the 2020 grid?

+-%cartesian_product
cartesian_product([])->[];
cartesian_product([OneList])->lists:map(fun(X)->[X] end,OneList);
cartesian_product([FirstList|RestLists])->
	Others=cartesian_product(RestLists),
	lists:append(lists:map(fun(Item)-> lists:map(fun(Rest)->[Item|Rest] end, Others) end,FirstList)).

+-%product
product(List)->
	lists:foldl(fun(X,Prod)->X*Prod end, 1, List).

p11()->
	Str="
	08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 08
	49 49 99 40 17 81 18 57 60 87 17 40 98 43 69 48 04 56 62 00
	81 49 31 73 55 79 14 29 93 71 40 67 53 88 30 03 49 13 36 65
	52 70 95 23 04 60 11 42 69 24 68 56 01 32 56 71 37 02 36 91
	22 31 16 71 51 67 63 89 41 92 36 54 22 40 40 28 66 33 13 80
	24 47 32 60 99 03 45 02 44 75 33 53 78 36 84 20 35 17 12 50
	32 98 81 28 64 23 67 10 26 38 40 67 59 54 70 66 18 38 64 70
	67 26 20 68 02 62 12 20 95 63 94 39 63 08 40 91 66 49 94 21
	24 55 58 05 66 73 99 26 97 17 78 78 96 83 14 88 34 89 63 72
	21 36 23 09 75 00 76 44 20 45 35 14 00 61 33 97 34 31 33 95
	78 17 53 28 22 75 31 67 15 94 03 80 04 62 16 14 09 53 56 92
	16 39 05 42 96 35 31 47 55 58 88 24 00 17 54 24 36 29 85 57
	86 56 00 48 35 71 89 07 05 44 44 37 44 60 21 58 51 54 17 58
	19 80 81 68 05 94 47 69 28 73 92 13 86 52 17 77 04 89 55 40
	04 52 08 83 97 35 99 16 07 97 57 32 16 26 26 79 33 27 98 66
	88 36 68 87 57 62 20 72 03 46 33 67 46 55 12 32 63 93 53 69
	04 42 16 73 38 25 39 11 24 94 72 18 08 46 29 32 40 62 76 36
	20 69 36 41 72 30 23 88 34 62 99 69 82 67 59 85 74 04 36 16
	20 73 35 29 78 31 90 01 74 31 49 71 48 86 81 16 23 57 05 54
	01 70 54 71 83 51 54 69 16 92 33 48 61 43 52 01 89 19 67 48",
	put(data,list_to_tuple(lists:map(fun(Tokens)->
				list_to_tuple(
					lists:map(fun list_to_integer/1,string:tokens(Tokens," "))) end,	
		string:tokens(Str,"\n\t")))),

	%
	% The four possible directions
	%

	D=[[0,1],[1,0],[1,1],[1,-1]],
	Ans=lists:max(lists:map(fun([X,Y,[Dx,Dy]])->
				product(lists:map(fun(S)->
					p11(get,X+S*Dx,Y+S*Dy) end,
					lists:seq(0,3))) end,
					cartesian_product([lists:seq(1,20),lists:seq(1,20),D]))),
	io:format("~w~n",[Ans]).

p11(get,X,Y) when X<21,Y<21,X>0,Y>0->
	element(X,element(Y,get(data)));

%
% The guard above and this default below allow for a simpler algorithm
% that can run off the edge, but isn't affected as those instances always
% evaluate to 0
%

p11(get,_,_)->0.

+-#cartesian_product
def cartesian_product(*a)
	return [] if a.length==0
	return a[0].map{|h|[h]} if a.length==1
	a.map!{|b| b.to_a}
	b=cartesian_product(*(a[1..-1]))
	a=a[0]
	res=[]
	if block_given?
		a.each do |aitem|
			res=res+b.select{|i|yield(aitem,*i)}.map{|i|[aitem]+i}
		end
	else
		a.each do |aitem|
			b.each{|bitem| res.push([aitem]+bitem)}
		end
	end
	res
end

+-#Enumerable
module Enumerable
  def sum
    self.inject{|u,v|u+v}
  end
  def product
    self.inject{|u,v|u*v}
  end
  def count(ob)
    self.select{|i|i==ob}.length
  end
  def take_while
    return [] unless yield(self.first)
    if(self.class==Range)
      evalPoint=self.first
      evalPoint=evalPoint.succ while yield(evalPoint.succ) and not evalPoint==self.last
      return self.first..evalPoint
    else
      s=self.to_a
      upTo=1
      upTo+=1 while yield(s[upTo]) and upTo<self.length
      return self[0...upTo]
    end
  end
end

$p11data="08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 08
49 49 99 40 17 81 18 57 60 87 17 40 98 43 69 48 04 56 62 00
81 49 31 73 55 79 14 29 93 71 40 67 53 88 30 03 49 13 36 65
52 70 95 23 04 60 11 42 69 24 68 56 01 32 56 71 37 02 36 91
22 31 16 71 51 67 63 89 41 92 36 54 22 40 40 28 66 33 13 80
24 47 32 60 99 03 45 02 44 75 33 53 78 36 84 20 35 17 12 50
32 98 81 28 64 23 67 10 26 38 40 67 59 54 70 66 18 38 64 70
67 26 20 68 02 62 12 20 95 63 94 39 63 08 40 91 66 49 94 21
24 55 58 05 66 73 99 26 97 17 78 78 96 83 14 88 34 89 63 72
21 36 23 09 75 00 76 44 20 45 35 14 00 61 33 97 34 31 33 95
78 17 53 28 22 75 31 67 15 94 03 80 04 62 16 14 09 53 56 92
16 39 05 42 96 35 31 47 55 58 88 24 00 17 54 24 36 29 85 57
86 56 00 48 35 71 89 07 05 44 44 37 44 60 21 58 51 54 17 58
19 80 81 68 05 94 47 69 28 73 92 13 86 52 17 77 04 89 55 40
04 52 08 83 97 35 99 16 07 97 57 32 16 26 26 79 33 27 98 66
88 36 68 87 57 62 20 72 03 46 33 67 46 55 12 32 63 93 53 69
04 42 16 73 38 25 39 11 24 94 72 18 08 46 29 32 40 62 76 36
20 69 36 41 72 30 23 88 34 62 99 69 82 67 59 85 74 04 36 16
20 73 35 29 78 31 90 01 74 31 49 71 48 86 81 16 23 57 05 54
01 70 54 71 83 51 54 69 16 92 33 48 61 43 52 01 89 19 67 48".split("\n").map{|s|s.split(" ").map{|i|i.to_i}}

def p11prod(x,y,d)
  dx,dy=0,1 if d==:down
  dx,dy=1,0 if d==:right
  dx,dy=1,1 if d==:diag1
  dx,dy=-1,1 if d==:diag2
  xs=(0..3).map{|i|dx*i+x}
  ys=(0..3).map{|i|dy*i+y}
  return 0 unless (xs+ys).all?{|i|(0...20).include? i}
  (0..3).map{|i| $p11data[ys[i]][xs[i]]}.product
end

def p11
  puts cartesian_product((0...20),(0...20),[:down,:right,:diag1,:diag2]).map{|t|p11prod(*t)}.max
end

def p11{
  val inp="""08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 08
    49 49 99 40 17 81 18 57 60 87 17 40 98 43 69 48 04 56 62 00
    81 49 31 73 55 79 14 29 93 71 40 67 53 88 30 03 49 13 36 65
    52 70 95 23 04 60 11 42 69 24 68 56 01 32 56 71 37 02 36 91
    22 31 16 71 51 67 63 89 41 92 36 54 22 40 40 28 66 33 13 80
    24 47 32 60 99 03 45 02 44 75 33 53 78 36 84 20 35 17 12 50
    32 98 81 28 64 23 67 10 26 38 40 67 59 54 70 66 18 38 64 70
    67 26 20 68 02 62 12 20 95 63 94 39 63 08 40 91 66 49 94 21
    24 55 58 05 66 73 99 26 97 17 78 78 96 83 14 88 34 89 63 72
    21 36 23 09 75 00 76 44 20 45 35 14 00 61 33 97 34 31 33 95
    78 17 53 28 22 75 31 67 15 94 03 80 04 62 16 14 09 53 56 92
    16 39 05 42 96 35 31 47 55 58 88 24 00 17 54 24 36 29 85 57
    86 56 00 48 35 71 89 07 05 44 44 37 44 60 21 58 51 54 17 58
    19 80 81 68 05 94 47 69 28 73 92 13 86 52 17 77 04 89 55 40
    04 52 08 83 97 35 99 16 07 97 57 32 16 26 26 79 33 27 98 66
    88 36 68 87 57 62 20 72 03 46 33 67 46 55 12 32 63 93 53 69
    04 42 16 73 38 25 39 11 24 94 72 18 08 46 29 32 40 62 76 36
    20 69 36 41 72 30 23 88 34 62 99 69 82 67 59 85 74 04 36 16
    20 73 35 29 78 31 90 01 74 31 49 71 48 86 81 16 23 57 05 54
    01 70 54 71 83 51 54 69 16 92 33 48 61 43 52 01 89 19 67 48"""
  val grid=inp.split("\n").map(_.trim.split(" ").map(_.toInt))
  var greatest=0
  for(i <- 0 until 20) {
    for(j <- 0 until 20) {
      for(d <- List((1,1),(1,-1),(1,0),(0,1))) {
        var p = 1
        try{
          for(x <- 0 until 4) {
            p*=grid(i+x*d._1)(j+x*d._2)
          }
        } catch {
          case e => p=0
        }
        if(p > greatest) greatest = p
      }
    }
  }
  println(greatest)
}